Hi Michael,

> seams, that extrusions from projected (not planar) curves are causing
> problems with caps and fillets.

In order for caps to be created automatically, the curves you are extruding need to be both closed and also planar.

MoI does not know how to automatically create a surface for the cap if the curve is not planar. In a case like that you'll have to create a surface some other way (like with a sweep or something) and then slice it with the extrusion to form a solid. If you have several surfaces intersecting each other with the inside core forming a solid you can use the Boolean Merge command to automatically trim all the pieces with each other and extract the solid inner piece.

But also if your shape is nearly planar you may want to use "Flat" snap to flatten it down to a plane so that it is truely planar and will then get the automatic cap behavior - to do that go to one of the side views and use the edit frame corner handle - drag it down slightly until you see the "flat" snap appear like so:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3378.4

- Michael