When used with Swfdec, WebKitGTK+ is showing rendering errors on a lot of pages which makes use of Flash.
For example, any YouTube page shows rendering problems, but is still useable, where as a site like http://thereifixedit.com is almost impossible to browse.
An uneducated guess is that this is bug 18831, but I'm filing this just to be sure.
I'm using Epiphany 2.28.0 WebKitGTK+ 188.8.131.52 and Swfdec 0.8.4.
Development of swfdec have stopped, and this bug is most likely a duplicate of bug 18831 so there's really no point in keeping it open.