When internal tab has it side face's lower edge coincident with the bend it fails to create the neck as a flat pattern but if the lower edge is set back by 0.1mm the flat pattern forms correctly?

However, it works perfectly on the outer tab. 

SW 2020 SP5.0.

Flat pattern - Outer tab retains bend radius. Inner tab looses bend radius.Folded - Outer tab. Edge coincident to the bend.Folded - Inner tab