>FWIW, it seems that this happens for packages that USE_GMAKE.  So maybe
>MAKE_PROGRAM and MAKE conflict?

Ah, that's a good area to look at - generally you need to take care 
to not propagate $MAKE from bmake to gmake environments - else 
bad things can happen.  So your problem may well relate to this.
Though why you only see it on certain platforms is "interesting".

--sjg