After the bug query http://bugzilla.xfce.org/show_bug.cgi?id=1694 I discovered that mouse1+control opens the context menu. I tried it on a launcher which has several items and it opened the context menu _and_ the sub-menus for the other items. Cheers :)
Hehe, good catch. Maybe I could pretend it is a feature...
Fixed in revision 21173, so it will be in the next beta release. Thanks.