I was testing bug 60816 by creating a post with bad HTML. When I clicked Preview the errorbox shows only
An unexpected error occurred.
clicking Reply gives a more helpful
An error occurred. The error message received was: Exception Caught: ID searchbox already defined
So exception reporting is inconsistent between preview and reply. I would lean towards providing more information.
The particular exception from bug 60816 should be fixed by 1.23wmf13, after that you'll have to find a different post error to reproduce this bug.
Version: master
Severity: minor