> Any idea what's happening.
Yes, I think I may.
Your assumption that the northwest corner of the dataset is -122, 33 is incorrect.
l3mapgen requires a rectangular shape when it generates it's output raster. The
input bounding coordinates are used to define that rectangle such that the output
will completely contain the defined region of interest. In your case, you have defined
a non-rectangular projection, so the output raster is larger to accommodate the ROI.
For this particular scene and projection, the lower left is -122, 3; lower right -72,3 as
you specified (happens that the widest part of the image matches the input).
However, the UPPER corners of the box are NOT -122, 33 and -72,33: