I can't repro this. Are you dragging the window a little when you click? I know Unity will de-maximize a maximized window if you drag it its title bar down.
No, I'm not dragging the window, it always happens with one single click. I also believe it has been like this since day one.
Maybe it is a problem on my end, if I have time tomorrow I'll reinstall Kubuntu and steam scratch and report back.
I can confirm this.
By the looks of it, in KDE 4.9, if you click and hold a maximised window at any point, it will de-maximise either after about a second, or when you move the cursor.
Steam windows do it instantly and without any cursor movement.
And it behaves oddly with clicks sent to a few top rows of a maximised Steam window. It seems to ignore it (that menu bar loses its "shine") and stay maximised and otherwise unmoving; other windows maintain the move/hold for a second behaviour.
Just an update on this issue.
Finally had the time and I reinstalled everything from scratch and was able to reproduce this issue.
Changed to Arch Linux 64-bit with KDE 4.10
Processor Information:
Vendor: AuthenticAMD
Speed: 2800 Mhz
3 logical processors
3 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: 3.7.9-2-ARCH
X Server Vendor: The X.Org Foundation
X Server Release: 11204000
X Window Manager: KWin
Steam Runtime Version: steam-runtime-release-i386_2013-02-22
Video Card:
Driver: ATI Technologies Inc. ATI Radeon HD 4770
Driver Version: 3.3.11672 Compatibility Profile Context
Desktop Color Depth: 24 bits per pixel
Monitor Refresh Rate: 60 Hz
VendorID: 0x1002
DeviceID: 0x94b3
Number of Monitors: 1
Number of Logical Video Cards: 1
Primary Display Resolution: 1920 x 1080
Desktop Resolution: 1920 x 1080
Primary Display Size: 18.74" x 10.55" (21.50" diag)
47.6cm x 26.8cm (54.6cm diag)
Primary VRAM Not Detected
Sound card:
Audio device: Realtek ALC889A
Memory:
RAM: 3954 Mb
Miscellaneous:
UI Language: English
LANG: en_GB-UTF-8
Microphone: Not set
Total Hard Disk Space Available: 146288 Mb
Largest Free Hard Disk Block: 125354 Mb
Installed software:
Recent Failure Reports:
This is now fixed. Since last beta update I think.
Nothing extracted yet.
Issue:
If a Steam window is maximized in KDE a single click on the top of the windows will de-maximize it.
Expected:
Double click should de-maximize the windows.
System Information:
https://gist.github.com/4642430
Kubuntu 12.10 64-bit
KDE 4.9.98