Currently the QML based thumbnails are not updated on damage events. This should be fixed by listening on the damage event for the thumbnailed window and triggering a repaint of the thumbnail area. Interesting offtopic note: this has been a regression for thumnails in Alt+Tab and nobody has reported it so far.
Git commit ea08542002d18d80f4af993599aeb0b21ded15a6 by Martin Gräßlin. Committed on 16/03/2012 at 12:33. Pushed by graesslin into branch 'master'. Repaint Thumbnail Item on window damage Allows to have live updates for thumbnails in tabbox. FIXED-IN: 4.9.0 REVIEW: 104301 M +8 -0 kwin/thumbnailitem.cpp M +1 -0 kwin/thumbnailitem.h http://commits.kde.org/kde-workspace/ea08542002d18d80f4af993599aeb0b21ded15a6