(Posting as a comment to this bug since I'm pretty sure it's the same root issue)
The Twitter hook doesn't seem to encodeURIComponent the tweet content before sending it to Twitter's API, so putting an ampersand in actually terminates it. See for instance https://twitter.com/WorldsMMO/status/506809682468421632 which was auto-tweeted from a commit message that said "Ensure player shooting sound & animation always plays". The tweet stops right before the ampersand.
Creation of new service integrations (including this one) was deprecated a while back in favor of Bitbucket Cloud's webhooks, Connect integration framework, and email notifications. As a result, we're closing this as Won't Fix.