Hmmm... Not seeing this issue here.
@bdeen-valve As in, you cannot reproduce, or I didn't explain myself clearly?
What I believe is happening, is that OpenGL tries to draw a 1920x1080 image, on both monitors, thus a 1920x1080 scaled to 3840x1080, so the width count as double when moving the cursor.
This means that when the cursor is 0 px from the left edge, the cursor is 0 px from the left edge. if I move the cursor 400 px right on the screen (so-so), the game registers the cursor as being at 800 px.
This means that the closer I get to the right border of my primary screen, the higher the offset is.
So lets say the menu when launching CS:S is 150px from the left border, and they're 200px wide. This gives me a clickable area from the left side of the screen 150px to 350 px.
If I move the cursor 200 px (visually clicking the button) the game registers my mouse at 400px.
Did that make sense?
EDIT:
I am using 2 monitors, with Nvidia TwinView.
Running Fluxbox.
I solved this issue myself, and it wasn't really an obvious one.
Last night I recompiled my WM (Fluxbox) with support for Xinerama (which I don't use), due to another issue I was having with mplayer.
I was told that maybe Nvidia Twinview functioned through Xinerama API, which led to misbehaving windows.
I recompiled Fluxbox with xinerama support, restarted Fluxbox, and here we go, a respecting OpenGL application.
Sorry :)
Nothing extracted yet.
EDIT: I just checked and this is the same with TF2, used to work in the first release of TF2
Description
When trying to configure games or connecting to a server, the mouse clicks wont be registered, leaving menus only usable through keyboard navigation.
Steps to reproduce
Debug
Systeminfo