This has been happening for about the last week, so I'm guessing it is an issue with the latest 7.3 release (which we really, really like by the way).
This is only happening on some cases and we are still trying to figure out the difference, but I thought I'd go ahead and throw it out there.
When we receive an email to our support address, it goes into FogBugz. We then reply and all is good. In the last week though, our support address has started getting added to the cc line when we reply. It doesn't happen every time. I'll try to figure out why that is, but in the meantime, I thought I'd throw this out there in case others were seeing this behavior too.
Updated: I think the issue has to do with the case of the email that they email to. In other words, when the e-mail to us with all lower case (support@estatesales.net), it puts it in the cc line. If they email to us with the casing like we have it in admin (support@EstateSales.NET), it works correctly and does not put it in the cc line.