Jetmail Monitor not keen on deleting mail

[Spam sucks]

I have been using the mail monitor for quite some time, having now upgraded to version 6.1.1. But my problem still lives on: I will mark mail to be deleted, but the first go will very seldom actually delete them, only the second time will they disappear. I tried to mark all at once, and I tried to mark AND delete one by one, no difference! With the amount of spam you get these days, it does mean quite a lot of extra work to have to do it twice over. Can anyone tell me why this is so and suggest a means of correcting this bug (or whatever it is).