Wayne, yes, I do turn out to have gnome do. Or had, since now it is completely removed. So I'll try this for a couple days. Thanks, this is the easiest first step.
Then if this doesn't work, or doesn't fully work, I will follow up with Phil's suggestions first on removing mono, and then on monitoring file access, which should get to the bottom of it. Many thanks for that too.
I do have mono installed, so that could be the next thing to go...
Peter