NetBSD TK70 question

[Christian Corti]

I'm not sure where I should start asking, so I'm starting here ;-)

I have a problem reading TK70 (and probably TK50) tapes in NetBSD 3.0 on a 
MicroVAX II. There is absolutely no way of reading a single tape block 
with a simple read(). All I get is
   mt0: unknown opcode 0x80 status 0xc01 ignored
on the console, and then the driver hangs. The output is generated in 
/usr/src/sys/dev/mscp/mscp.c
It is my impression that the code has *never* been tested on real hardware 
after all that years. BTW the TK70 is working fine otherwise (e.g. I can 
boot the MVII diagnostic tape).
Now for something strange: the same procedure works in SimH (with the same 
system installation and kernel). So apparently SimH has a "bug", too. It 
doesn't behave like the real device.
Background of the story: I want to image TK70 tapes as TAP files.

Has anyone ever encountered the same behaviour?

Christian