I figured out my problem with the Mitsubishi adapter and the culprit is comcast. it only took two days of playing around with the adapter. By accident I was playing with the adapter while on a high def channel that was not broadcasting in 3D. Son of a gun, the adapter gave me top and bottom and side by side options. When I went to the on demand channel and loaded the 3D movies (I tried all four) the adapter would not "adapt". In frustration I checked the resolution of the supposedly HD on demand movies and discovered that I was receiving them in 480i. I then tried the PGA 3D on demand replay, which was in high def and the adapter worked.
So, I called comcast and asked if they were aware that these movies were being broadcast, at least here in south Jersey, in 480i. The service rep who I talked to said he would look into the problem and get back to me. Hopefully, the movies will be transmitted in HD.
The user manual that came with the adapter advises that for automatic detection of HDMI 1.4a 3D signals I should use 3D mode Normal. Well, the choices I have are SbS, TtB and 3d off, which I suppose is the normal mode. I guess I will find out soon enough.