So, I know this doesn't answer your question - yet. I was trying to find what code cycles through the 5 "modes" you mention in your question, and this is what I've found so far.
It looks like you've found a bit of a can of karmic worms.
It appears that the Fn-F8 key is getting ignored within dell-wmi.c - I see an error to /var/log/messages each time I press it: dell-wmi: Unknown key 42 pressed - so the code to switch monitor configurations isn't being called from there.
With nothing plugged into the external VGA port, here's what I'm seeing in /var/log/messages when I hit Fn-F8:
Dec 2 14:27:02 RStops-PBR kernel: [26143.201120] dell-wmi: Unknown key 42 pressed
Dec 2 14:27:02 RStops-PBR kernel: [26143.430158] i2c-adapter i2c-2: unable to read EDID block.
Dec 2 14:27:02 RStops-PBR kernel: [26143.430163] i915 0000:00:02.0: HDMI Type A-1: no EDID data
Dec 2 14:27:02 RStops-PBR kernel: [26143.435023] i2c-adapter i2c-2: unable to read EDID block.
Dec 2 14:27:02 RStops-PBR kernel: [26143.435026] i915 0000:00:02.0: HDMI Type A-1: no EDID data
Dec 2 14:27:02 RStops-PBR kernel: [26143.439499] i2c-adapter i2c-4: unable to read EDID block.
Dec 2 14:27:02 RStops-PBR kernel: [26143.439502] i915 0000:00:02.0: HDMI Type A-2: no EDID data
Dec 2 14:27:02 RStops-PBR kernel: [26143.443954] i2c-adapter i2c-4: unable to read EDID block.
Dec 2 14:27:02 RStops-PBR kernel: [26143.443958] i915 0000:00:02.0: HDMI Type A-2: no EDID data
Dec 2 14:27:02 RStops-PBR kernel: [26143.490877] [drm] TV-25: set mode NTSC 480i 0
Dec 2 14:27:02 RStops-PBR kernel: [26143.632555] [drm] TV-25: set mode NTSC 480i 0
Dec 2 14:27:03 RStops-PBR kernel: [26144.621183] i2c-adapter i2c-2: unable to read EDID block.
Dec 2 14:27:03 RStops-PBR kernel: [26144.621187] i915 0000:00:02.0: HDMI Type A-1: no EDID data
Dec 2 14:27:03 RStops-PBR kernel: [26144.625648] i2c-adapter i2c-2: unable to read EDID block.
Dec 2 14:27:03 RStops-PBR kernel: [26144.625652] i915 0000:00:02.0: HDMI Type A-1: no EDID data
Dec 2 14:27:03 RStops-PBR kernel: [26144.630157] i2c-adapter i2c-4: unable to read EDID block.
Dec 2 14:27:03 RStops-PBR kernel: [26144.630159] i915 0000:00:02.0: HDMI Type A-2: no EDID data
Dec 2 14:27:03 RStops-PBR kernel: [26144.634866] i2c-adapter i2c-4: unable to read EDID block.
Dec 2 14:27:03 RStops-PBR kernel: [26144.634870] i915 0000:00:02.0: HDMI Type A-2: no EDID data
Dec 2 14:27:03 RStops-PBR kernel: [26144.680947] [drm] TV-25: set mode NTSC 480i 0
Dec 2 14:27:04 RStops-PBR kernel: [26144.822361] [drm] TV-25: set mode NTSC 480i 0
After that I see some number of odd pulseaudio messages:
Dec 2 14:27:36 RStops-PBR pulseaudio[2436]: ratelimit.c: 1 events suppressed
(Note though that I'm on a Dell Latitude E6500 notebook, not an XPS M1330)
I'll keep poking at this as time permits and post a followup if/when I find anything.
-pbr