Out of curiosity I checked the message status to an other user who is using Mobility (Nokia E71). I am amazed, event the Read/Reply status is updated in GroupWise, just the order is a bit wired:

Third-Party Downloaded - Wed, 21.04.2010 01:34
Replied - Wed, 21.04.2010 02:05
Read - Wed, 21.04.2010 02:58

First Reply, then Read ;-)
Guess that is because the Reply is sent immediately by Mail for Exchange, while the status update is done during the regular (set as hourly) sync...

BTW: no "Concealed Subject" problems on neither Nokia E71 nor Motorola Milestone...