GIF export flakey?

[Michael L. Waddell]

Is there a trick to exporting a simple chart to GIF? I'm trying to 
export a simple, single-color (black), no-shadow, no-transparency 
flowchart to GIF, using only objects from the Basic palette, and it's 
breaking up some of the graphics. What's bizarre is that if I view the 
exported GIF in Preview or GraphicConverter, it looks completely 
fubar'd...but if I view it in Internet Explorer, it looks *mostly* ok, 
still with some artifacts. I'm using OmniGraffle 2.1.1, however I also 
had the problem in 2.0.8. Any input would be appreciated.

MLW