I see the very same thing using openSUSE 12.1, the KDE 4.8 desktop and using the nVIDIA proprietary video driver. It just takes one more step to take the application out of filling the whole (2nd) screen. It might be a desktop thing, but I am not sure to whom you would complain about for this somewhat minor occurrence.
Ah… This happens here (nvidia blob + KDE 4.8.4) when I drag a window bigger than the monitor I’m dragging it to - my second monitor is smaller than the first. If the window is smaller than the monitor size it doesn’t go fullscreen.
I don’t think its driver related, for (as another data point) I could reproduce it with a setup using the OSS radeon driver (KDE 4.8, 12.1) … perhaps KDE or X bug.
I do believe you are on to something regarding the different sized monitors - specifically their display resolutions. For example, I used to get this moving windows from my smaller (but oriented, via rotation, with a larger height resolution of 1280px) 2nd monitor to my larger (but with a smaller height resolution of 1200px) primary monitor.
Very annoying to say the least. Couldn’t find a KDE setting that might of been affecting it (was thinking along the lines of edge-snap-window-to (for a lack of better terminology) type stuff)
(I no longer have this system configuration … though, I could reconfig as such, but it would be a major PITA to switch from my current setup, so I’m not volunteering to do so http://forums.opensuse.org/images/smiliesnew/tongue.png )
Perhaps not, but it’s always in good form to give relevant specs, like OS, DE, video driver, etc. I think it’s more in the way KDE4 deals with multiple monitors, but it could also be related to nvidia’s twinview and not to xinerama - I think ATI uses something like it. Does nouveau uses twinview or it’s open source equivalent, if any - randr perhaps? I don’t know, I’ve used nouveau very rarely…