On a Debian squeeze amd64 system, I am unable to use any disks in drives on the Beta 128 interface. Any attempt to use them just responds "No disk", whether inserted using "Insert New" or "Insert" from an already existing file.
This has been tried in trunk revisions 4726, 4624 and 4553 - with the result the same every time.
Could you try the Beta Disk smoke test described in peripheral_tests.txt? I can't see any malfunction.
Hmmm... this appears to be gone again... both in release 1.1.1 and revision 5058.