It asks immediate after login to change the screen with RandR.
X11.app: main(): argc=5
argv[0] = /Applications/Utilities/XQuartz.app/Contents/MacOS/X11.bin
argv[1] = :3
argv[2] = -once
argv[3] = -query
argv[4] = IP-of-sun
Waiting for startup parameters via Mach IPC.
X11.app: No launchd socket handed off, unsetting DISPLAY
X11.app: do_start_x11_server(): argc=5
argv[0] = /Applications/Utilities/XQuartz.app/Contents/MacOS/X11.bin
argv[1] = :3
argv[2] = -once
argv[3] = -query
argv[4] = IP-of-sun
[4169079.114] Xquartz starting:
[4169079.114]
X.Org X Server 1.13.0
[4169079.114] Build Date: 20120927
[4169079.128] Initializing built-in extension Generic Event Extension
[4169079.128] Initializing built-in extension SHAPE
[4169079.128] Initializing built-in extension MIT-SHM
[4169079.128] Initializing built-in extension XInputExtension
[4169079.128] Initializing built-in extension XTEST
[4169079.128] Initializing built-in extension BIG-REQUESTS
[4169079.128] Initializing built-in extension SYNC
[4169079.128] Initializing built-in extension XKEYBOARD
[4169079.128] Initializing built-in extension XC-MISC
[4169079.128] Initializing built-in extension SECURITY
[4169079.128] Initializing built-in extension XINERAMA
[4169079.128] Initializing built-in extension PseudoramiX
[4169079.128] Initializing built-in extension XFIXES
[4169079.128] Initializing built-in extension RENDER
[4169079.128] Initializing built-in extension RANDR
[4169079.128] Initializing built-in extension DAMAGE
[4169079.128] Initializing built-in extension MIT-SCREEN-SAVER
[4169079.128] Initializing built-in extension DOUBLE-BUFFER
[4169079.128] Initializing built-in extension RECORD
[4169079.128] Initializing built-in extension X-Resource
[4169079.128] Initializing built-in extension XVideo
[4169079.128] Initializing built-in extension XVideo-MotionCompensation
[4169079.128] Initializing built-in extension GLX
[4169079.128] x: 1680, y: 0, w: 1920, h: 1178
[4169079.128] x: 0, y: 240, w: 1680, h: 1050
[4169079.170] (II) GLX: Initialized Core OpenGL GL provider for screen 0
[4169079.249] X11.app: DarwinProcessFDAdditionQueue_thread: Sleeping to allow xinitrc to catchup.
[4169079.289] (EE) Error loading keymap /tmp/server-3.xkm
[4169079.290] (EE) XKB: Failed to load keymap. Loading default keymap instead.
[4169083.680] noPseudoramiXExtension=0, pseudoramiXNumScreens=2
[4169084.286] noPseudoramiXExtension=0, pseudoramiXNumScreens=2
[4169084.317] xpbproxy: can't open default display
[4169084.317] xpbproxy thread is terminating unexpectedly.
[4169110.254] noPseudoramiXExtension=0, pseudoramiXNumScreens=2
...
[4169270.724] noPseudoramiXExtension=0, pseudoramiXNumScreens=2
[4169421.127] Server terminated successfully (0). Closing log file.
with XQuartz 2.7.4 (reinstalled with Installer) I get exactly the same output but there is no requester where XQuartz asks to use RandR. The screen extends over both screens.
...
...
If I try to change to this resolution nothing happens (in 2.7.1. there is the RandR-Requester ...)
I hope, you can get me a hint. Until then I go back to 2.7.1