After a little more investigation this weekend, I think I found the root cause.
 On cayman, 128bpp surfaces require non_disp ordering for hw access to both
linear and tiled surfaces.  When we use the 3D engine we can set the non_disp
ordering on both the tiled and linear sides (via CB or texture), but when we
use the DMA engine, we can only set the non_disp ordering on the tiled side, so
after a L2T operation with the DMA engine, the data ends up in the wrong order
on the tiled side.