Bad render for PNG

[Naetius]

Hello all,

I've compiled succesfully mozilla-gtk2 from ports, everything
goes well except for PNG images that are rendred in a very
bad way... (shot: http://www.timworld.org/supporto/pnginmoz.png)
This problem does not affect the rest of the system, like Gnome.
Where could be the problem?

Thanks in advance.

PS: Mozilla 1.3.1