[Daiya Mitchell]

I think it's by design. Because Word uses the size of the Balloon Text
when doing the superfast screen drawing computation about how big to
make the balloons. Or somesuch. It would be nice if it were mentioned
in Help--but my Help doesn't say anything about how to change the
appearance of the comments at all (MacWord 2004).

Jim wrote:
By the way, this STILL applies in the newly released Word 2007 (which is
where I had my problem) - and there seems to be no clear official help or
information regarding this peculiar quirk.