raster calc introducing unpredictable shifts

Discussion created by sjskhalsa on Feb 25, 2014
I'm reprojecting a DEM to the MODIS Land grid, and find horizontal shifts in the output. I'm using raster calculator with just the DEM as input and environmental variables to specify output coord system (with snap to grid on), cell size, processing extent - using a MODIS file (MCD12Q1) to get proj info, extent, snap-to grid and raster cell size.

The really weird thing is that I have two DEMs (both derived from SRTM, having same CRS) and I get different shifts, using the same operation (doing replay from the results log, just replacing the input file name) in the outputs (difference field show hillshade effect).  If I difference the inputs, there are no shifts evident.

What the blazes is going on?