Version: (using Devel) OS: Linux Installed from: Compiled sources When I maximize an app-window (whether by double-clicking on the titlebar, or through the button in the titlebar), the app-window does not maximize 100% horizontally. The app leave about 1cm (on 12" screen running at 1024x768) empty area on the right side of the screen. If I manually resize the window, I can make it fill the entire screen, however. It looks like Kwin is thinking that there is a panel in the side of the screen, but no panel is present.
Which KDE version were you using? Is it still happening? I'm experiencing a similar situation, but vertically with KDE 4.3.3. It seems that there is a "invisible panel" on the bottom of the screen (I use me panel on the top) and windows don't maximize correctly. I tried changing my "real" panel to the bottom, but it didn't change the empty area. Testing with another user, the problem doesn't happen, so I suppose it's caused by something wrongly saved in my .kde.
Well, the problem was something in plasma-desktoprc . As it didn't happen with plasma-desktop killed, it's probably a plasma bug, not a kwin one.
I rember about this plasma bug and it should have already been fixed on the plasma side.