Created attachment 93507 [details]
1. Load attached testcase (which is a modified version of <http://www.vdat.com/techsupport/PRNwindowstest.asp>)
The audio for the movie plays, but the video doesn't. And if you have Aero disabled and drag a window in front of the plugin area, you see pixel garbage accumulate there because the plugin isn't painting.
This bug only occurs in WebKit2, not WebKit1
WebKit1 works around this (and a crash that doesn't seem to happen in WebKit2) using the PluginQuirkRemoveWindowlessVideoParam quirk.