I am having the same problem here... PLUS: I also have the same problem when a user replies to you reply once again. No email is sent.
When the admin replies to a support ticket, I get the following line in maillog:
Apr 16 00:32:56 production sendmail: l3FMWuEM022437: from=admispconfig, size=250, class=0, nrcpts=0, msgid=<200704152232.l3FMWuEM022437@production.vhos ts.nl>, relay=admispconfig@localhost
When replying as user the a reply from admin I get the following line in maillog:
Apr 16 00:34:19 production sendmail: l3FMYJdf022590: from=admispconfig, size=286, class=0, nrcpts=0, msgid=<200704152234.l3FMYJdf022590@production.vhos ts.nl>, relay=admispconfig@localhost
(which is actually the same...)
In other logs nothing in particular is written.
I'm wondering: is this a bug, or a 'feature'?