X forwarding work, x program output goes to /dev/null?

[tg%gmplib.org@localhost (Torbjörn Granlund)]

This is a strange problem.  I routinely use

  ssh -X somemachine

and then e.g., do

   vncviewer [blahblah]

or some other X command.

On a new system, running netbsd 7 beta under xen 4.5, everthing works
except that the X command seems to be sending its output to /dev/null.
No error message anywhere, just nothing displayed.

A possible cue is logged to pflogd:

14:39:36.891003 IP6 localhost.65514 > localhost.6014: Flags [S], seq 20778400, win 32768, options [mss 33588,nop,wscale 3,sackOK,nop,nop,nop,nop,TS val 13 ecr 0], length 0

IP6?  I only really desire to talk IP4 with this box, and I haven't set
any IP6 addresses or configured any pf rules.  How can I say "please
stick to IP4 until I say otherwise"?


Torbjörn
Please encrypt, key id 0xC8601622