[Proj] bug in cs2cs or what?

[Greg Troxel]

  I'm trying to convert 3 points from WGS84 to local datum and I noticed that
  during the datum change phase the coordinates are the same.

  $ cs2cs -f "%.4f" +ellps=WGS84 +proj=geocent +to +towgs84=-199.0,74.0,246.0
  +ellps=GRS80 +proj=geocent < WGS84_XYZ.txt ; more WGS84_XYZ.txt 

Try datum=WGS84 instead of ellps.  proj no longer does datum conversions
for the case of two ellipsoids, not sure about this case.  I wonder if
proj should error out if given towgs84 and and ellipsoid, if this is
really what's going on.