Presumably you've checked for nasties ?
Virus'sss etc...?
If no other suggestions come to light, it may possibly be worth going to Spyware Warrior ? ( Brilliant computer global "Help" community site, free (donation if you want), absolutely straight, and a very good bookmark to have anyway. )
They handle a fair few strange happenings, but whether they could help with this, I don't know, but they are really good, and have helped me and others with seemingly insurmountable computer-based problems totally successfully.
Having said all that, you probably know about 'em anyway !
