Baud rate cycling problem under 4.1bsd

[Rex Sanders]

  We have a Vax 750 with 16 line Emulex CS21 running 4.1bsd.  We would
like to cycle our plugboard ports between 4800-1200-300 baud.  Seemed
like a very straightforward modification to getty and /etc/ttys.
  However, if you hit BREAK at 4800, the line dies and it takes a
reboot to bring it back to life.  Even tried arranging it to go
300-1200-4800, and you can break from 300 to 1200, but you hang again
breaking from 1200 to 4800.  Other combos (e.g. 9600-1200-300) work.
Am I missing something here?  Any clues are welcome.

-- Rex
   ucbvax!menlo70!sanders     RSanders.Pascalx @ Denver (Arpanet)