It was infact tty related and NOT 'maxusers' related.  Special thanks
to a great and wise old hacker Eric Schnoebelen for pointing this one
out.

Basically, when you run MAKEDEV to up the number of PTYs, be sure to
add those new entries to /etc/ttys (should be MAKEDEV's job anyway??)

a for i in tty?? in /dev should do it, but be careful you'll match to
random serial devices (about 14 devices actually) which will be 
obvious when you look at them .. 

If putting this into MAKEDEV is 'okay' I would be happy to do a PR with
a diff.

SMJ