Joris,
I'm one of the Bitbucket Server developers. While another team handles the actual smart commits functionality, and will need to be the ones who ultimately action this ticket, I just wanted to offer a quick workaround for you.
From the way your merge log looks, I'm going to guess you have commit messages like this:
(The exact breakup of the lines isn't super important; I'm guessing it's something like that, though.)
If you add a blank line before the first smart commit directive, git merge won't include anything after that in the merge log. This is a Git behavior, and outside the control of Bitbucket Server. Git calculates the "summary" of a commit message to be everything (including line breaks) until the first blank line. So a message like this would just show as "CAR-5494" in the merge list:
It's not my intention to imply you're "doing it wrong", or that getting the developers to change the way they write commit messages would be simple (or even necessarily desirable for your overall workflow). I just wanted to offer you a way around the behavior that doesn't need to wait for code changes.
Hope this helps,
Bryan Turner
Atlassian Bitbucket
This issue required a fix in JIRA. As a result, the fix is dependent on the JIRA version connected to Bitbucket Server. Upgrade to JIRA 7.1.9+ to get the correct behaviour with merge commits.