To reproduce compile and run the attached testcase. It turns a simple pipeline
(videotestsrc ! xvimagesink) from playing -> ready after doing 50 iterations and
to playing again.. Expected behaviour is that the pipeline just continues when
going to playing again. Instead the output window turns black and stays that way
untill the users moves the window a little... 

I've tried to track it down in the xvimagesink element itself. When one comments
the XFillRectangle call in gst_xvimagesink_xwindow_clear all is fine. But i've
got no idea why that's the case. As this is also called when doing the first
null -> playign transition