When the panel is in autohide mode. If you try to open a file by dragging it onto a launcher icon. The panel wil not enlarge therby rendering the operation imposible. This has been a problem since versions 4.3.x. Thanks alot for all your hard work...
Thanks for the report. I guess it's just one of those things that slipped my mind when porting features from 4.2 to 4.4. It's fixed with revision 24990 in SVN, so it should be available for the next update of Xfce.