HorusUK,
Do you use any filters in Mail Monitor or just use SpamPal to filter spam?
I use to have this problem also, but it has not happened recently. It happened a lot when I used Mail Monitor's filters for spam. Since I switched from SpamPal to Spamihilator, I do not need Mail Monitor to filter spam anymore. Spamihilator puts spam into its own recycle bin and it can be deleted there, before it gets to Mail Monitor.
I only use filters to put emails into categories. I'm not sure if any of this has anything to do with the problem you are having, but it is interesting that after I stopped filtering for spam in Mail Monitor, the problem seemed to stop. ???
BTW - I'll put this at the other post you referenced also.