Then mouseover from bottom, both, thumbnail scroller and maincontrols will hide out, with current settings:
Thumbnail scroller, autohide: off
Maincontrols, autohide: on
Maincontrols, locktothumbnails: on
Then turn off autohide from maincontrols, anything will works fine.
Update:
Same story on thumbnail scroller with opacity of the thumbnails when inactive, - opacity don't return back. Does not depend on the value of autohide.
Update #2:
When autohide_offset set to 0, - thumbnail scroller does not show up on mouse over.