The xtUML team uses Redmine for issue tracking. At the open-sourcing of BridgePoint, we evaluated Redmine as the best of the free and open issue trackers. One Fact customers use it to report service requests. The overall community uses it to report BridgePoint bugs and then to assign, participate and track progress. Redmine has nice project management features. Overall, Redmine is getting better all the time. So far, our team is happy with the choice of Redmine.
https://support.onefact.net/ takes you to the xtUML issue tracker.