Hi, Magician

I talked to some staff about this, and was about to reply to your PM today

I tested that, and my archive messages goes up by 2, instead of 1, if that's what you mean. It appears to be a software bug. As Chipster said, I'm sending a support ticket to the developers.
EDIT: And the the support ticket has been sent! It takes time for them to reply, so let's hang in there.
Thanks for pointing it out!