Batch in Town Hall reported #1
The forums are reporting #2
http://forums.cerb4.com/showthread.php?t=2849
There's something in common for those installs where a ticket mask isn't available during the reply. It could potentially just be a cached template.
I've committed a fail-safe anyway that will fall back to the internal ID of a ticket if no mask was provided.
Verified fix itself forces the ticket ID into the URL and that clearing the cache seems to eliminate the root problem.
Closing out.
5.0.0-pl1 (Build 2010060701)