Hi!
I've found that if floppy is busy by running VMWare and I try
format it, than dosemu silently exits. There is message
in boot.log with -D9+d:

---
INT13: disk=0 ah=0x8 dp=0x83c1180
disk get parameters 0
INT13: disk=0 ah=0x18 dp=0x83c1180
disk: set media type 0 failed, 18 sectors, 80 tracks
...
INT13: disk=0 ah=0x3 dp=0x83c1180
ERROR: (disk) can't open /dev/fd0: Device or resource busy
leavedos(22|0x16) called - shutting down
---

Can we just ignore busy disk if it is floppy?
(See attachement)

-- 
Grigory Batalov