January and February are our busiest times here in the support trenches, so we aren't able to drop in on the user forum as much as other times of the year. Sorry about that - you didn't get ignored on purpose! Neil is right though, this is mostly a forum for users to discuss amongst themselves. Whenever you have a bug report, you should contact us directly, either at (800) 486-1800, or at email@example.com
That said, I took your issue to development, we looked at the code, and it is indeed a bug, and it has been there since 8. However, this is the first time we've heard anything about it, since that particular combination (alternate addresses + mail merge) isn't an everyday thing for a lot of people, and it's not something that would be immediately obvious, unless you were really paying attention (which you obviously are!). I don't want to sound like I'm finger wagging or anything, but why didn't you tell us sooner? We would have had it fixed two versions ago if we'd known. We do testing inhouse, and we even have public beta testing to help make a very solid product. However, no amount of testing is going to turn up everything that folks who actually use the software every day can find.
I've got it listed in our bug tracker now, and if it's not fixed in the next maintenance release (I'm not sure how close that is to being ready), it should be included in the following one.