bug #150363 talks about a problem with media-plugins/gst-plugins-mad-0.10.4, which is the unstable version. Stable version (0.10.3)has the same bug, at least in two cases (me and the last comment in bug #150363), and the same patch works for this, so please patch it in portage. I opened a bug because I can't reopen the other one.
thanks fixed in 0.10.3-r1