[Coco] Can't copy real floppy to CoCo-SDC on a CoCo 2

[mike at borncoco.com]

I'm having an issue with CoCo-SDC on a CoCo 2. I have an MPI (unmodified), with SDC in slot 1 and FD-501 Floppy in slot 4. It comes up SDC-DOS 1.2 CC2. I can mount drives and access things on the SD card just fine. However, if I issue the Drive command to access a real floppy, I loose access to the SDC and even the "DIR -" command returns an error as though SDC-DOS has vanished. I'm just trying to copy a real floppy to the SDC:

DRIVE 1,"MYDISK.DSK"
DRIVE 0,OFF

At this point I can do a "DIR 1" (SDC), and a "DIR 0" (real floppy) without issue.

However, as soon as I issue the "BACKUP" command, the CoCo 2 behaves as though SDC-DOS has vanished. 

BACKUP 0 TO 1

This results in the CoCo2 attempting to copy real floppy 0 to real floppy 1. And the "DIR -" & command returns "?SN ERROR". I can still use "DIR" to see the floppy disks. 

Has anyone run into this issue??

Thanks,
-Mike