If a comment consisted of only XML-like syntax (such as "<test>"), it would be treated as if the comment was completely empty and the comment would be canceled. The issue here is that reviewCommentFormIsEmpty would strip out tags before testing whether the comment was empty or not. Removing the call to stripTags() fixes the bug.

I manually tried to recreate the bug with different ways.

By submitting '<sim realtime="true>' or 'something <sim realtime="true>' in the comments you can verify that the bug is no longer exists.