Hi Dan - that looks like a triangulation failure by those importers.

Are you exporting from MoI as N-gons? (that's the Output: option on the meshing options dialog at export time).

Some programs have difficulty dealing with complex N-gons (N-gon means polygon that has more than 4 points in it) that are made up of a whole lot of points and have concave shapes. Renderers will usually need to triangulate those n-gons at some point during rendering or import, and unless that triangulation process is done very carefully it is easy for it to have bugs that produce bad output with triangles kind of leaking to the "outside" of what is supposed to be the outer boundaries of the polygons.

To fix it, when exporting from MoI switch the Output: N-gons option to be Output:Quads & Triangles instead.

That will make MoI itself generate a triangulation of complex polygons instead of relying on the other programs to do it, and MoI should be able to do a better job of it.

Please let me know if using the "Output: Quads & Triangles" option does not solve the problem.

- Michael