Fix Version/s: None
VBox 4.3.40 with VBEMP
-install Spotify (it will launch automatically after install and will be maximized)
-install Opera 12.18 (it will launch automatically after install and will be windowed)
-activate the apps in alternating order via their taskbar pane
They draw correctly including their titlebar
-When Opera is activated, it will not draw its titlebar (unless you enforce a refresh explicitly by moving the window)
Up to here I thought this was 100% reproducible (Spotify eating, explorer eating not).
After experimenting with that for more than an hour, I came to the conclusion that this is a race condition. There is a slight chance that Spotify will not eat up Operas taskbar as well.
I guess the reason for Spotify triggering that so nicely is, that it takes longer to draw its stuff than other apps.
Eventually this relates or is same than CORE-15024, but I can not say for sure.