Hmmm, testing fillet (using V1.1 demo)...

filletbu1.3dm
I can't fillet around the sphere shapes.

filletbu2.3dm
Seems to fillet perfectly.

filletbu3.3dm
Seems to fillet perfectly.

filletbu4.3dm
I can fillet around the blob shape, but I can't fillet around the sphere shape - nothing happens.

filletbu5.3dm
Seems to fillet ok... but I notice you have the lines broken up into a few pieces...

-EDIT-

Also, quick question Michael...

With filletbu5.3dm, as the following picture shows, the curve on top is made up of 3 curves...



Is there any way to connect them together?

I've tried join, but that just creates a new curve separate from the object itself...