The problem is the same one as the old rshd bug, but it isn't in rshd. I have
suffered under the rshd bug which make me think this problem was more wide
spread than it really is. I did test this under a number of environments, so I
was fairly sure the descriptor wasn't being inherited by bash.

It turns out the gdb seems to be doing the same sort of thing that rshd used
to do. Because the behaviour of the two problems is identical I thought they
were the same problem. I don't quite know why this problem doesn't manifest
itself when gdb is is run from (a clean) tcsh, but I think it has to do with
the SHELL environment variable.

I intend to rebuild the latest bash and gdb for the machine in question, and
then see what happens.

Cheers,
Lloyd