I was needing for a big customer of my company a mechanism that fires some action on certain transitions.

Thus I was quite happy to notice that the next version of trac (0.11) provides a way to customizes workflows. And thanks to the Advanced Ticket Workflow Plugin, to fulfill me need.

BUT, since there is always a but... it was not working ....

After quite some time and a lot of debugging I figured out why : the brand new workflow system was bugged, and the transition action can only be fired on a "non status change" transition. I have pointed it out to the developer of the plugin, explaining him the files that were in cause... Fortunately it has been modified in the trac sources right now... Thanks to me, like it is said :)