Help me understand auto-switching

I have a Panny VT20 with a UVerse source. The panny will only show ESPN3d in 3d if I manually switch the 3d mode to side-by-side.

I then have to switch it back to auto once I want to go back to 2D programming.

I would expect this when going through my Onkyo 605 AVR, but I get the same results while going directly from the STB->TV (via HDMI of course).

So who's to fault? The Uverse STB or the television. I'd guess that the UVerse box is to blame, as I doubt they are passing some flag telling the TV that the content is 3d and in side-by-side.

I just want to understand how the auto-switching process should work.

That's what I figured. Does it do this regardless of the programming being shown? I've only tested while the channel is off-air and that static slide is up saying ESPN 3D.

Do you know if the box has to send a flag giving this information?