Thanks for sending that in, the geometry library that I'm using seems to have some problem with calculating the fillet in this case. I'm going to have to collect this up and send it over to them when I get a batch of examples.

In the meantime as a workaround you can duplicate those edge curves there (select them, then copy/paste), then do a curve fillet and then revolve the curve fillet into the fillet surface you're looking for, then trim that into place. Let me know if you want details on how to do this.

- Michael