Fails to boot DOS from any drive except C:

[froller]

This is not actually a bug in RetroBoot rather than in MS-DOS and PC-DOS.
But I have to find a workaround or RetroBoot renders useless.

[froller]

I tried to intercept Int 13h to fake loading of MBR and change order of partitions or "active" flag but had no luck. Either MS-DOS 6.22 reads more than 1 sector at a time or I was getting screwed setting interrupt handler.

[froller]

Looks I really got screwed because of DOS overwrites memory region where my forged Int 13h handler is located.
Seems I need to intercept Int 12h to reserve some memory for my handlers. Or intercept Int 2Fh to pretend RetroBoot is RPL (but this will screw real RPL if any)