PNG export doesn't seem to pay attention to the state of the "inverted" setting for layers. It's apparently confused about the difference between polarity and inverted. Me too, but copying the draw logic from gerbv.c results in the following patch (to 1.0.1 or 1.0.2) that appears to make export work correctly.
2007-09-20 06:32:39 UTC in gerbv -- a Gerber (RS-274X) viewer
