Entering ffmpeg in any of the search boxes on the main bugzilla page brings me directly to bug 172950 (which was closed in 2007) rather than to the expected page of search results. Using the search page gives the expected list. Reproducible: Always
I found that bug 172950 had "ffmpeg" in the Alias field. I removed the alias from that bug and that seems to have fixed this. I'm not sure if normal users have access to modify the Alias field.
I don't see anything about aliases on the bug, but it's possible I'm looking in the wrong place or something. Anyway, you seem to have fixed it.