In vertical panel background of active application gets corrupted sometimes. Instead of even blue-ish background i get background that looks like made of multiple blue-ish transparent shapes of irregular sizes. Closing application window and opening it again fixes background problem temporarily.

Reproducible: Sometimes

Steps to Reproduce:
1. Make a vertical panel
2. Add icons-only tasks widget
3. Select launchers of test applications to be visible when application is not running
4.1. Cause a hidden application (like instant messenger hidden in the tray) receive notification or
4.2 Open application by clicking pinned icon on taskbar 

Actual Results:  
Sometimes background will become like this: http://imgur.com/U1O45b3 (left to right: inactive with notification, hovered by mouse, active).

Expected Results:  
Backgrounds in all cases should be of even color.