> Hmmm, that is disappointing. I sort of assumed that Modo would be more robust in this area, as best I can tell right now those seem to be bugs in Modo's handling of ngons.

> I've attached a file here that contains just that single 5-sided ngon. Can you please test this with modo and see if it will read it or not?

I don't exactly know where the problem comes from, but I can confirm that models made out of quads and triangles only are correctly imported in Modo.
Your 5-sided ngon imported fine (see image)...
I'll continue my MoI to Modo experiments in the coming days... ;-))

Cya