I'm seeing this as well, seems to be in BZ 459756 and 471450. It seems
as though at least some DNS servers get confused by the parallel AAAA
and A queries and only respond to one of them. The worst part is that
the nature of the problem will make it hard to update to a fixed
implementation. I think this particular issue is worth a mention in
Bugs/F10Common because it seems to be relatively wide spread (seems to
be impacting comcast users reliably).