The output vector's GetElemWithCornerSet method is incoherent: for tetra it returns maxcorner=4 and for wedge maxcorner=6. In the help it is stated right underneath that tetra results are stored in 1,2,3,5.
This is impractical when retrieveing corner output, computing new output and reinjecting it using the same maxcorner info previously given.
Both GetElemWithCorner( ) and GetElemWithCornerSet( ) on the Output object have been changed to return the true "maxcorner" value for the next release. So, for a tet-only model maxcorner will now be 5, no longer 4. Hope this helps.