Random mail movement and duplication

Every few weeks or sometimes months I see a very strange set of conditions. I will find that large numbers of mails have been either either moved/copied into other folders or duplicated multiple times or both things together.

I never seem to lose any data, but it's a pain trying to sort it out.

These aren't folder that are even close to adjacent in the stack, so it's not finger trouble on my part.

Any one else experienced this or are the aliens who steal all the odd socks just persecuting me?

BB