Extremes Component bugs after "Fillet" on Closed Curve

Fellow GH Users,

I've found a bug using "Extremes" component and I would like to know if someone has ever experienced this one. 

Basically, whenever I apply a fillet to a Closed Planar Curve, the Extremes component gets lost and gives 2 times the same point for Low and High, as shown on the screenshot below. Whereas it was working fine before appying the Fillet.

It may be similar to an issue mentioned earlier on this forum about an issue using Extremes on Arcs.

Any help would be appreciated,

Thanks