I don't know if replying to my own post is bad form, but there's a thread herethat might explain what's going on.
I've just checked my registry and I appear to have two sets of OneDrive ovelays:
OneDrive1 ~ OneDrive5
(i.e. with six leading spaces before the word OneDrive) and
OneDrive1 ~ OneDrive6
(Just one leading space, and six of them, rather than five).
These are in addition to three keys for adobe and two others that I assume are used by Windows (EnhancedStorageShell and Offline Files)
I'm wondering if it mght be worth completely uninstalling OneDrive, manually deleting any leftover overlays in the registry, and then reinstalling it.