accept-process-output returns t and doesn't run sentinel

[Stefan Monnier]

I'm having a problem with URL failing to fetch pages via https which seems
to boil down to the following:

url-retrieve-synchronously calls

  (accept-process-output proc)

which returns t immediately (even though there was nothing received from the
process) and doesn't run the sentinel.  AFAICT the process-status is `signal'.

The process was created with `open-tls-stream'.

Does anybody have an idea why accept-process-output would immediately return
t even though it didn't get any output (and this happens repeatedly in
a loop until I cause the loop to exit via C-g)?
It's on an amd64 machine running some kind of Fedora 4 GNU/Linux system.


        Stefan