When you recieve the toast telling you have new mail, Plus! can/will also change the Windows' recieved mail count in the registry. I start to get the feeling this is the problem (also because it doesn't happen when you click the test button in the pop3 preferences in Plus!), though this feeling can be completely wrong of course
...
Something like you (Plus!) don't have the proper access rights to change it (typical stuff for Vista), or the location is slightly different for your Windows (would surprise me), or you even have a bad registry image, or whatever (all just guesses though)...
I don't know for sure anymore and I can't check, but I thought Plus! had some registry setting which could turn off the automatical update of Windows' new email count.
Would be nice to hear more about all this from Patchou.
/ 
