For some reason alt+f4 doesn't always closes the topmost window

Hello!

When a new window pops up (e.g. I launch an app), it becomes the topmost window, however for some reason it doesn't always gets the focus so, in this case when I hit alt+f4 it closes some other window in the background.
The taskbar tells correctly which window is the active, but I consider this as a bug since I meant to close the topmost window. This behaviour needs some extra time, extra attention from the user before hitting alt+f4.

Doesn't happens always, but happens quite often.

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: gnome (not installed)
ProcVersionSignature: Ubuntu 2.6.32-32.62-generic-pae 2.6.32.38+drm33.16
Uname: Linux 2.6.32-32-generic-pae i686
Architecture: i386
Date: Tue Jun 14 11:58:26 2011
InstallationMedia: Ubuntu 10.04 "Lucid Lynx" - Release Candidate i386 (20100419)
ProcEnviron:
 PATH=(custom, user)
 LANG=hu_HU.utf8
 SHELL=/bin/bash
SourcePackage: meta-gnome2