Fillet edge works, blend edge no. Why?

I tried to run a fillet edge (one unit, for example) and this works.
On the other hand, if I do a blend edge, this does not correctly fill the fittings. Is it a bug to fix? (Also the chamfer is not well executed).
(Rhino 6)
blend edge incorrect.3dm (250.7 KB)

Hello - added



Thanks Pascal, this defect also occurs by executing a Chamfer edge …

I would like to further clarify that the defect of the “fillet/blend edge” is also present on only one edge (on that (a) or on the one (b)).