DM Taskbars are always on top even if some application goes to full screen example YouTube video. On main mointor after full screen taskbar (generic) is invisible but on additional monitors DM taskbar is on top and covers (for example) YouTube player bar.
YouTube player [Adobe Flash Player] - issue exists
Twitch.TV player [Adobe Flash Player] - issue exists
VLC Player - issue does not exists (fullscreen VLC covers DM taskbar)
Diablo 3 - issue does not exists
So it appears that it's Adobe Flash Player issue but not 100% sure.
Tested on: Windows 7 x64