QPNGHandler does not read PNG images with DirectClass on big-endian machines

When compiling Qt on PowerPC platforms, Qt will generally be able to draw properly its graphics.
However, some PNG images will be loaded correctly, and some won't.
Attached are two pictures that will show correctly on a regular PC, however the second one will show incorrect colors on the PowerPC platform.
The main difference between the two as shown by ImageMagick's identify tool :
frame_0001.bad.png PNG 451x368 451x368+0+0 8-bit DirectClass 129KB 0.020u 0:00.019
frame_0001.good.png[1] PNG 451x368 451x368+0+0 8-bit PseudoClass 256c 88.7KB 0.000u 0:00.000

It seems DirectClass PNG are always shown incorrectly, while PseudoClass do not cause trouble.