Hello Michael.

Using one of the last example you have posted for @BRUNO I've found a strange filleting issue.
Before doing the fillet I first changed the model unit to millimeters (but also with centimeters the issue remains).

Here you can find the 3dM file : http://take.ms/L9Khy

1) I applied a INSET command to one face of the solid : NO ISSUE
Those are the INSET options I used :



2) I tried to FILLET the four corner edges of the inset : FAIL
I have used any kind of filleting options but without success. The FILLET commands never ends and it only display "CALCULATING..."

I've tried also with V4 and instead I get immediately a "CALCULATION FAILED" response

This is the V3 screenshot :





3) I've repeated the experiment with Rhino 6WIP.
I simply copy/paste the model from Moi.

With Rhino V6WIP the fillet performs but with BAD result :



As you can see here the resulting objects is a "polysurface" not a "closed polysurface" :




4) I've repeated the experiment with Rhino 5.
I simply copy/paste the model from Moi.

In this case the fillet performs WELL, as you can see.






Any kind of help or suggestion will be much appreciated :)

Thanks.