Hi Yenmonger, so I investigated your fillet problem here.

The closed surfaces are actually completely smooth where they are closed, there is no tangency break in either one of them.

That little extra fillet segment that I was showing earlier just comes from how Fillet works, part of the fillet calculation involves creating offset surfaces and then intersecting the offsets.

If you take these 2 surfaces where the surface seams are touching:



And then offset them (here by 0.05 units, with "Flip" enabled):



You can see there that the offset surfaces do not have their seam edges touching each other anymore, which is just part of having things meet at an angle.

Anyway, that's what is causing the fillet to be made in some segments.

The actual bug here seems to be either in surface/surface intersection or somewhere deep down in the edge filleter.

Often times in circumstances like this you can work around a problem in the edge filleter by separating things into individual surfaces and selecting 2 surfaces to do a surface/surface fillet calculation rather than an edge based one.

There was a problem though in this case where that was not working, the surface/surface fillet mechanism was bailing out because it thought the intersection curves were intersecting each other. I've removed that particular bail-out for the v2 final release, so in the v2 final surface/surface intersection will work for this case, here I show it on your original model (separated into surfaces), with a radius of 0.05:




Let me know if you still need help with that fillet, and if you let me know what radius you want I can produce it for you now with the surface/surface fillet.

- Michael