KSnapshot started to capture rectangular region boundaries and size toolbox when compositing is enabled. Only in SNA mode.
KDE Bugs team says it's xf86-video-intel bug.
Please see this https://bugs.kde.org/show_bug.cgi?id=320476
Once again KDE/Qt and kwin amaze me by their inefficient rendering. At least it found a bug in my code. The issue here is that kwin continues to render the static composited image (that is the cause of the black flash), and the DDX failed to undo its shallow copy of the scanout used by ksnapshot for its region selection GUI.
Author: Chris Wilson <email@example.com>
Date: Sun Jun 2 12:13:46 2013 +0100
sna/dri: Undo any COW before performing a copy with DRI2CopyRegion
Signed-off-by: Chris Wilson <firstname.lastname@example.org>
@Chris: if you notice any wrong behavior in KWin please let us know. The only way to improve the code is if the information is passed on from more experienced people.