Hi Mark,

I don't think it's Gmail doing that, as my other account (this main one, Exchange-hosted) also does it, and IIRC from back then, a Yahoo test account also did. 

Unless if you already checked that part of the code, it looks like the Send Follow-up code bit is using the original sent-in email subject field to populate the catch-up email subject, not the "processed/posted" one that went out with the tag added, and it may have to do with whether one replied to the topic through email or online, IIRC catch-up messages from the same person would exhibit this; or, the code is just "forwarding" the original message as it came in, not as it "posted" on the topic archive, if that makes sense.  And it only happens when catch-up messages are being sent right after following an unfollowed-before topic, not under normal-flow (send-after-posted) follow messages.

Please give me a bit of time to follow a couple of new topics and generate the catch-up messages and do some research; there's got to be some pattern to this that should help point out what's going on.

Cheers,
Christos