python.org renders fine at first load, but scrolling makes it unusable: lots of white areas and bits and pieces of the original page. It is visible on the main page, but easier to reproduce on eg. the PEP pages (https://www.python.org/dev/peps/). This behaviour is confirmed with webkit-gtk-2.11.9{0,1} on X11. These pages used to leak loads in older versions. It's probably not just python.org, but that's the only example I encountered so far.
This looks fixed in 2.11.92 .
Then it was probably bug #155426. *** This bug has been marked as a duplicate of bug 155426 ***