problem with Mapserver WCS handling of NaN?

[Jeff de La Beaujardiere]

The Web Coverage Service (WCS) feature is (sort of) working
on our installation, now that our sysadmin recompiled --with-wcs.

However, the not-a-number (NaN) values in the floating-point GeoTIFF
data files used as input do not seem to be handled correctly.

- When the GeoTIFF is a single global dataset, the NaNs are converted
to zeroes. I can filter those out of these particular data only
because the valid data are all in a range > 0.

- More seriously, when there are multiple GeoTIFF files enumerated
in a tile index, the NaN areas overwrite data from earlier GeoTIFFs,
even though the WMS component handles this properly. For example,
this test image was generated via WMS:
http://www.map.nasa.gov/test/soar/wms-nans.png
The no-data areas are blank and transparent, as desired
(the black rectangle has something to do with my attempt to classify
the raster data, but is a different problem than the NaN problem).
This test image was generated from the WCS output:
http://www.map.nasa.gov/test/soar/wcs-nans.png
The no-data areas are opaque zeroes that hide valid data
from other granules.

Thanks for any help,
Jeff DLB