MacOS X cocoa emacs always opens new frames on main display of multi-headed system

[fooreg]

I recently upgraded from Emacs 23.4.1 to 24.1.1 (specifically emacs-app from 
Macports) on my multi-headed MacOS 10.6.8 machine. With the previous version, 
newly created frames appeared on the same display as the frame holding the 
current focus. Now all newly created frames always appear on the main display 
(the one showing the menu bar and dock). I see this issue when I type "C-x 5 2" 
or I evaluate "(make-frame)" or software like VM and ERC creates new frames. 
For example, when I'm in VM on the right display and visit another folder, the 
new summary/presentation frame appears on the middle display.

I compiled 24.1.1 from the official source using "--with-ns" and saw the same 
behavior.

I've managed to resolve other upgrade issues by identifying things like 
settings in obsolete variables, but I've seen no mention of this problem. Can I 
get Emacs 24 on this system to work the way my older version did?