Sometimes window preview generated on mouse hover in unity launcher stays displayed and on top after the unity launcher hides. To remove it you have to refresh the preview by moving the mouse cursor over the app icon in the launcher one more time. See attached screenshot.
ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: unity 4.22.0-0ubuntu3
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic 3.0.4
Uname: Linux 3.0.0-12-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 1.23-0ubuntu3
Architecture: amd64
CompizPlugins: [core,bailer,detection,composite,opengl,imgjpeg,decor,compiztoolbox,regex,move,winrules,place,imgpng,mousepoll,resize,grid,vpswitch,gnomecompat,session,animation,wall,unitymtgrabhandles,workarounds,fade,thumbnail,expo,scale,scaleaddon,unityshell]
Date: Thu Oct 13 12:10:53 2011
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release amd64 (20101007)
SourcePackage: unity
UpgradeStatus: Upgraded to oneiric on 2011-09-27 (16 days ago)
Status changed to 'Confirmed' because the bug affects multiple users.