Hi renklint, the difficult thing with CAD data transfer is that different CAD programs can represent trimming boundaries in different ways and one of the biggest things is that some allow a trimming edge to cross over the "seam" of a closed surface while others (including MoI and Rhino) don't allow a 3D edge curve to cross over the UV seam.

So there is some conversion processing that happens particularly with trim boundary edges on closed surfaces. The conversion involves some fairly tricky operations to cut edges at the seam crossing. There are various situations that can make that cutting difficult like if an edge runs nearly coincident to the seam edge but meanders back and forth slightly, things like that.

- Michael