problem with resampling 16-bit data

[mpg@…]

We've noticed a problem with reprojecting full 16-bit images when using 
biliner or bicubic: the output image is speckled, presumably due to 
over/underflow.  As verification, using the 20041210 snapshot we recklessly 
replaced all occurrences of "GInt16" with "GUint16" in gdalwarpkernel.cpp and 
the problem went away.

The command line to reproduce is just:
  gdalwarp.exe -t_srs EPSG:4326 -rb f.tif ff.tif
where f.tif is a simple 1-banded, 1Kx1K, unsigned, 16-bit geotiff -- whose 
dynamic range uses all 16 bits.

I'll attach the two images if I can figure out how, otherwise I can email them 
as required.