System message: "changed title" shows raw markdown code
### Summary
Since a few days, GitLab.com shows raw markdown code in system messages.
Screenshot:
### Steps to reproduce
See system note before this issue comment: https://gitlab.com/gitlab-org/gitlab-ce/issues/21480#note_112034849
### Example Project
https://gitlab.com/gitlab-org/gitlab-ce
### What is the current *bug* behavior?
Raw markdown sourcecode is shown instead of rendered text.
### What is the expected *correct* behavior?
Render the markdown code into expected text with e.g. colors.
### Relevant logs and/or screenshots
### Output of checks
On GitLab.com.
### Possible fixes
I suspect this behavior is related to putting \{-text-\} into a bold \*\* environment.
Test1: {-**test**-} -> outer: color; inner: bold
Test2: **{-test-}** -> outer: bold; inner: color
issue