Hi I'm doing a typical random stab in the dark here, so
ponder it and then wait for Kenn's reply...
When you run r.resample the new GRASS cell file might
be GRASS compressed (run length encoded).
That means that bands of white (at the top and bottom)
would take fewer bytes than the number of cells.
Read the GRASS manual on r.compress and try uncompressing
the file (on a copy perhaps?). See if that does the
trick.
-sue