Sonoma or OCLP Bug? Preview doesn't release opened (but now closed) file

Seems too obvious to be an unfixed Sonoma Preview problem but I can't see how it is an OCLP problem either.

Mount an external drive with 3 partitions on it, use Preview to view files which are then closed. I can't unmount one of the partitions, no error message, one time the driver icon vanished, other times it just stays there.

Using lsof on the command line (sudo lsof /Volumes/MyVolume) shows a list of files kept open by Preview (the files were not open or visible). Closing and reopening Preview allows my drive to be cleanly unmounted.