Update :
Well, I've now had the opportunity to burn another CD-ROM, this time with "Auto insert notification" enabled.
Everything proceeded as before, ImgBurn burnt the disk, opened and closed the drive, then successfully verified it. After exiting ImgBurn, Windows Explorer showed the disk as blank, with 648MB capacity (it's actually a 700MB disk).
However, after opening and closing the drive again, the disk appeared correctly in Windows Explorer (and tried to "autorun", of course).
So, whatever the problem may be, the "Auto insert notification" process does put things right.
Joe.