strange fillet ?

 From:  PaQ
Ok here's an other 'hey, I didn't expected that'.
For the story I was just showing MOI to a friend, I was really happy to show how easy this piece of software is.
Just drawing some curves, doing an extrude, sliding (boolean merge) ... and did a 'magic fillet' ... but I wasn't able
to explain this :)

Of course I've tried different fillet size. I know filleting is an heavy task etc ... but still, it's not like I was doing a crazy one. I would even prefer to have a failed output that a wrong result :P

The construction scene is provided.

(workarounds are: use g1blend fillet or rebuild the wrong part by hand (sweep works perfectly here) ... but I still think that circular method should work too, as it works in an other package starting with an R and finishing by INO ^^)

EDITED: 3 May 2014 by PAQ