Magic Lantern + external monitor

I tried Magic Lantern on my Canon 60D, using a Marshall V-LCD651STX monitor with composite input, and the blow-up focus box that ML produces was unusable - it looked as if it were in the middle of a "venetian blind" wipe effect the whole time, with horizontal bands across it.

Has anyone been able to use ML with an external monitor, and is there a trick to it?

Bob C