Comment # 6 on bug 91998 from Daniel Scharrer

Both this and and the POSTAL 2 issue come from the same root problem - an Inf
or NaN returned by POW for vertices 'behind' the spotlight (dot(spot_direction,
vertex_direction) < 0):
http://cgit.freedesktop.org/mesa/mesa/tree/src/mesa/main/ffvertex_prog.c#n954

*** This bug has been marked as a duplicate of bug 91342 ***