Whoops! Forgot to refresh tab before posting. Redundant post follows:
Didn't wilderness have a post just a few days ago asking the same question?
The final asterisk effectively destroys the rule because it makes the period optional in exactly the place where you need it to be mandatory:
and that's all.
The leading anchor kills the rule in a different way, because "MSIE" never comes at the very beginning of a UA string. Well, except for the occasional robot.