I've investigated a bit further and come to the following conclusion.

Recent File works, but only if the drive that the file was saved on is running at the time that you start up Poser. Usually I power up Poser before powering up my USB external drive. Consequently Poser doesn't bother to tell me that I have previously opened or saved files on that drive. If I switch off Poser, then power up the USB drive and then start Poser again, I find that Poser has permanently lost all record of the recently opened files on that drive, though it lists the files on the other fixed drives.

It is therefore slightly more use than an ashtray on a motorbike, but not a lot.

Incidentally, the manual says that Recent File lists the last ten files that you've opened, but it alo lists any new ones that you have created and saved. The manual should therefore say "opened or saved".

Is there an easy and reliable way of reporting this bug officially?