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Tab vs. Supdup

I am trying to implement a Supdup terminal emulator for use over
RS-232 lines.  To debug this, I have been using TELNET through MINITS
to OZ, then doing @term supdup, which seems to almost work right.

When using EMACS, I did the following thing: on a line containing only
two words, separated by a tab, I did M-Rubout on the first word.  I
was subsequently rewarded with:

?Illegal instruction 104000,,76 at 41475 - JSYS error:
?Terminal cannot perform VTS function

It doesn't seem to happen unless the tab is there, by which I infer
that EMACS wants the terminal to perform the tab.  Obviously Supdup
can't do this.

So what's wrong?  Since Supdup works fine over the network, it must be
the case that @term supdup doesn't do the right thing.  Further, it
should not be possible for this error to happen -- I shouldn't have
been able to set my terminal type to Supdup in the first place if it
wasn't meant to be done.

A couple of other problems -- OZ does not recognize the Supdup input
escape character, so I can't use the extended character set or flow
control, both of which I want.  Also, on dialups, there seems to be no
way to turn off parity, so I lose the eighth data bit and subsequently
cannot use Supdup.  This seems pretty silly since there are eight bits
going one way (the meta key on Ambassadors), and only seven bits going
the other.  It seems unlikely that the terminal will check the parity
in only one direction.