I discovered something similar...
If you install Stardock's "START 8" menu in windows 8... and then hide the taskbar from the object settings options... it hides the start 8 menu also.
BTW: Personally I think that if you pay them money for Objectdock... it should include all the features of "start 8" so that you don't need that. Just an added bonus to entice buyers to buy objectdock instead of only the start 8 menu tool. Although only while you use the objectdock "start" docklet.