Pe locks USB drive even after closing any files on it

[eblanca]

This is reproducible: open a local file, then plug an USB drive and modify a file stored onto (now you will have two Pe windows), then save and close it (again with a single Pe window).
From now on, you won't be able to unmount the USB drive until all Pe's windows will be closed, as the resource will appear as "busy".

[OscarL]

For the record, not limited to USB drives. Same happens with other mounted partitions on the same disk too. (I've just hit this one).