bug#15037: Display can't be opened (display newer than emacs session)

[Sewall, Jason]

I have a long-running emacs session with a server running on it (24.2.1, on 
Fedora 18). I have started up a new VNC session on the host, creating DISPLAY 
:1.0, but emacs refuses to let me create a frame on it: 

M-x make-frame-on-display <RET> :1.0 <RET>
Display :1.0 can't be opened

If I start a new emacs session with emacs (with -Q or not) and run the above, 
the frame is created.

I am not an expert in emacs frame handling nor in X, but it seems like emacs is 
reading the available displays when it starts up and refuses to connect to 
anything that started up after it. I'm happy to provide more info as needed. 

Cheers,
Jason