Loading disk images with MegaFlashROM, AUTOEXEC.BAS is gobbledygook

Of course , but for the openmsx users at least it solves the problem.
That cartridge solves some other similar situations .

That's good to know for at least checking out stuff in OpenMSX!

I've been going through some other disks, and most of them actually have worked fine with MAPDRV. It seems I was really unlucky with the couple of disks I picked at first :-P