If you're busy coding such things why not take a peak at what might be causing the bug!
MediaPortal is open source so you can easily get access to the code via SVN.
Sorry, not my specialty. Besides, this program can be used in any program, not just MP. And, I'm sure much wiser minds than mine are working on the bug.
Default everything with the inbuilt TV-engine. I uninstalled the SVN and went back to RC3 an hour ago, but now it works (i.e. Autohide works perfectly again).