Frozen playback - external (HDMI) and main monitor

Hi guys, here's a stumper

Problem:

When the TV is connected, and only when the TV is connected, playback results in a still frame on both the canvas and the external TV. Audio plays fine, and stopping playback immediately produces the new frame according to the playheads position on both display locations. Scrubbing the video works seemlessly for both displays and the program doesn't lag or feel overworked.

My CPU usage rarely exeeds 15% during playback, and sits at a comfy 3% when the program is idle. RAM is also in good supply.

I recently purchased a Mophie minidisplay to HDMI adapter so that I can use my Samsung TV as a preview monitor while editing. Everything is working great and I've got my TV set up as a second display. Graphics are fine with virtually no lag when using a majority of applications for video based playback. Except for FCP. This is the first time I've used this computer with external monitoring, however my previous MBP was able to handle this just fine using an adapter from AVI to DVI and then to HDMI.

Fixes that didn't work:

- A good number of sequence presets, the goal being to match the output resolution with the sequence

- All combos of settings in Audio/Video Settings->AV Devices

- Various combos of options in System Settings->Playback Controls->Video Quality

Current Settings:

Color LCD Monitor Resolution: 1680 x 1050

SAMSUNG HD TV: 720p

System:

FCP 7.0.3

MBP w/ Lion 10.7.2

2 GHz Intel Core i7

4GB 1333 MHz DDR3

AMD Radeon HD 6490M 256 MB

External HD for scratch, project, media

Any help or advice would be greatly appreciated!

Have at it!