Fillet corners bug: generates open and invalid curves

See the attached. Filleting in Rhino works as expected, yet grasshopper leaves me with invalid and open curves. I hope this can be fixed, but suggestions for a workaround is also welcome.fillet-corners-bug.gh (85.0 KB)

this seems to solve it, so I wonder what are the settings behind the built-in fillet corner tool

fillet-corners-bug-workaround.gh (88.4 KB)