Yes, 2.6.1 beta1 does work better. I read the top entry in the changelog and mistakenly thought it was for the latest release! My bad. I did get to the bottom of the problem. A program was written such that it would fail if both png 1.4 and 1.5 .pc files co-existed on a machine, regardless of sym links. Installing XQuartz 2.6.0 triggered the problem, but was not the cause.