XWindows curiosity with two cygwin instances

[Jim Garrison]

I have my normal Cygwin+Cygwin/X instance at c:\cygwin64.  I've
temporarily set up another instance (no X) at u:\cygwin64.  I notice
that if I start up the X server on the first instance, X programs
started under the second instance cannot connect to the XServer.
They always get, for example:

jim@HOME10 ~
$ xclock
Error: Can't open display: :0

But this works just fine if I run the same command in a mintty window
launched under the first instance.

This happens even with "Disable access control" set, and also
"xhost +".  I also tried DISPLAY=localhost:0 but that doesn't
work because the X Server isn't listening on port 6000.

Is this an artifact of how Cygwin/X emulates unix sockets?

What option do I need to change to have the XServer listen on
port 6000?

TIA

-- 
Jim Garrison jhg@acm.org