Also similar glitches:
Strange textures (happens as with crossbow, f. e. in few seconds texture restores, then switches back again):

Flashlight. Bad texture renders only on certain surfaces

Same machine, same specs.

I have the same issues (scope + textures)

Also I'm not sure if this is related but I can also always see the Stalker monster that is supposed to only be visible at close range.

Here are my specs:

Processor Information:
    Vendor:  AuthenticAMD
    Speed: 3000 Mhz
    6 logical processors
    6 physical processors
    HyperThreading:  Unsupported
    FCMOV:  Supported
    SSE2:  Supported
    SSE3:  Supported
    SSSE3:  Supported
    SSE4a:  Supported
    SSE41:  Unsupported
    SSE42:  Unsupported

Network Information:
    Network Speed:  

Operating System Version:
    Linux (64 bit)
    Kernel Name:  Linux
    Kernel Version:  3.6.10-1-ARCH
    X Server vendor:  The X.Org Foundation
    X Server release:  11301000

Video Card:
    Driver:  NVIDIA Corporation GeForce GTX 560 Ti/PCIe/SSE2

    Driver Version:  4.3.0 NVIDIA 310.19
    Desktop Color Depth: 24 bits per pixel
    Monitor Refresh Rate: 59 Hz
    VendorID:  0x10de
    DeviceID:  0x1200
    Number of Monitors:  1
    Number of Logical Video Cards:  1
    Primary Display Resolution:  2560 x 1440
    Desktop Resolution: 2560 x 1440
    Primary Display Size: 23,50" x 13,23"  (26,97" diag)
                                            59,7cm x 33,6cm  (68,5cm diag)
    Primary Bus: PCI Express 16x
    Primary VRAM: 1023 MB
    Supported MSAA Modes:  2x 4x 8x 16x 

Sound card:
    Audio device: Realtek ALC889

Memory:
    RAM:  3956 Mb

Miscellaneous:
    UI Language:  English
    LANG:  fr_FR.UTF-8
    Microphone:  Not set
    Total Hard Disk Space Available:  488385 Mb
    Largest Free Hard Disk Block:  422330 Mb

can confirm all of these.
Core 2 Duo. Geforce 9600 gt, 310.19

I suffer from the same thing, creossboiw sometimes work, but when it don't it doesnt come back on. Sometimes the lens becomes completelly black, sometimes black with "reflections" (two white gradient spots), and sometimes black with a thin see-throug vertical stripe, but its not in the middle of the lens so it's' anyway pretty useless:P

Processor Information:
    Vendor:  GenuineIntel
    Speed: 3401 Mhz
    8 logical processors
    4 physical processors
    HyperThreading:  Supported
    FCMOV:  Supported
    SSE2:  Supported
    SSE3:  Supported
    SSSE3:  Supported
    SSE4a:  Unsupported
    SSE41:  Supported
    SSE42:  Supported

Network Information:
    Network Speed:  

Operating System Version:
    Ubuntu 12.10 (64 bit)
    Kernel Name:  Linux
    Kernel Version:  3.5.0-21-generic
    X Server vendor:  The X.Org Foundation
    X Server release:  11300000

Video Card:
    Driver:  NVIDIA Corporation GeForce GTX 670/PCIe/SSE2
    Driver Version:  4.3.0 NVIDIA 313.09
    Desktop Color Depth: 24 bits per pixel
    Monitor Refresh Rate: 60 Hz
    VendorID:  0x10de
    DeviceID:  0x1189
    Number of Monitors:  1
    Number of Logical Video Cards:  1
    Primary Display Resolution:  1920 x 1080
    Desktop Resolution: 1920 x 1080
    Primary Display Size: 20.04" x 11.26"  (22.95" diag)
                                        50.9cm x 28.6cm  (58.3cm diag)
    Primary Bus: PCI Express 16x
    Primary VRAM: 2048 MB
    Supported MSAA Modes:  2x 4x 8x 16x 

Sound card:
    Audio device: AV200

Memory:
    RAM:  15992 Mb

Miscellaneous:
    UI Language:  English
    LANG:  en_US.UTF-8
    Microphone:  Not set
    Total Hard Disk Space Available:  1290046 Mb
    Largest Free Hard Disk Block:  256285 Mb

I don't have that problem. I tested the three settings of scope model: Model (Low), Textured and Model (High):

• Model (Low):
  
• Textured:
  
• Model (High):
  

Also, i tested these parts of London Map with problems, but i haven't anyone:

However, i have other textures problems, i have them every time, with all settings tested from lowest to highest:

• Some skins are messed, it is the "Two face like" model (And has the https://github.com/ValveSoftware/steam-for-linux/issues/334 positioning issue too)
  
• Trader don't have a transparent glass in front:
  
  But in some case have anything directly:
  
• And Stalker aren't invisible, have a T-1000 looks like for a problem with the transparency
  

I think it isn't Steam fault, Tripwire should do some tweaks (or something more) and we need to say those problems directly too http://forums.tripwireinteractive.com/showthread.php?t=86698
The game is playable and nice like Windows but have some glitches.

Finally, my specs: KUbuntu 12.04.1, KDE 4.8.5

Información sobre el procesador:
    Fabricante:  GenuineIntel
    Velocidad: 1998 Mhz
    Procesadores lógicos 2
    Procesadores físicos 2
    HyperThreading:  No compatible
    FCMOV:  Compatible
    SSE2:  Compatible
    SSE3:  Compatible
    SSSE3:  Compatible
    SSE4a:  No compatible
    SSE41:  No compatible
    SSE42:  No compatible

Información sobre la red:
    Velocidad de la red:  

Versión de Windows:
    Ubuntu 12.04.1 LTS (32 bits)
    Nombre de kernel: Linux
    Versión de kernel: 3.2.0-35-generic-pae
    Editor de X Server: The X.Org Foundation
    Versión de X Server: 11103000

Tarjeta de vídeo:
    Controlador:  NVIDIA Corporation GeForce Go 7300/PCIe/SSE2

    Versión de controlador: 2.1.2 NVIDIA 304.48
    Densidad de color del escritorio: 24 bits por píxel
    Frecuencia de actualización del monitor: 60 Hz
    Identificador del fabricante: 0x10de
    Identificador del dispositivo: 0x1d7
    Número de monitores: 1
    Número de tarjetas de vídeo lógicas: 1
    Resolución de pantalla principal: 1280 x 800
    Resolución de escritorio: 1280 x 800
    Tamaño de pantalla principal: 11,38" x 0,83"  (11,38" diag)
                                            28,9cm x 2,1cm  (28,9cm diag)
    Bus principal: PCI Express 16x
    No se ha detectado la memoria VRAM principal
    Modos MSAA compatibles: 2x 4x 16x 

Tarjeta de sonido:
    Dispositivo de sonido: Analog Devices AD1986A

Memoria:
    RAM:  2013 Mb

Varios:
    Idioma de la IU:  Español
    LANG:  es_ES.UTF-8
    Micrófono:  Not set
    Espacio total en disco disponible: 23732 MB
    Bloque libre más grande en el disco: 7678 MB

Software Instalado:

Informes de fallos recientes:

This is some of my texture problems:

This is the only character which failed here.

No problems with any of the shop windows in any of the Manor-map shops, showing only one of them.

T-1000 texture problem :P But here crossbow lens works just fine.

Suddenly this happens to the crossbow

And it suddenly comes back in the same game, yet another texture problem of another basterd in the background there.

Another weird lens texture failure, happen at the end and the way to the shop shows.

M99 AMR lens did exactly the same as the crossbow lens, yet I forgot to make a screenshot of it, but it's likelly that they use the same type of texture in that lens as the others. Sometimes work, sometimes not.

System settings is pasted here before, in-game settings is running on "Highest"

LukasThyWalls, for missing textures try to look into log. There should be something about it.
AFAIK in UE1 (don't know about UE2) if texture is missing map will not load.

I think it isn't Steam fault, Tripwire should do some tweaks (or something more) and we need to say those problems directly too http://forums.tripwireinteractive.com/showthread.php?t=86698

Well as far as I know Ryan Gordon did the port, not Tripwire.

So this place is as good as any to report Killing Floor bugs really.

I wonder, Are any of these glitches reproducible in KF mod for UT2004?
I don't have UT2k4 installed. And I played KF mod only 2 minutes (because no one plays it online).
UPDATE:
I bet it is render issue. I took a look in KF System/ directory and I haven't found OpenGLDrv.so, but OpenGLDrv.dll!
There are no any of linux native modules at all! Seems they are built in killingfloor-bin (its size ~11.6 MB).
So I have two questions. Why was linux version built in this way? Why are there windows binaries?
UPDATE2:
I have analyzed log file and was unable to find any warnings about missing textures.
So I cannot explain it ATM.

We only can do to post all the bugs here http://forums.tripwireinteractive.com/forumdisplay.php?f=60

My KF textures problems are posted here http://forums.tripwireinteractive.com/showthread.php?t=87291 with KillingFloor logs attached as well.

Nothing to do here.

Don't worry. I've contacted Icculus and he says that they are working on this bug.