Only one node type can remove reciprocating reference

Odd issue I'm struggling with immensely, help greatly appreciated.

I have two node types with node ref fields that have been set to reference each other in the CNR configuration screen.

From Node A I can successfully add and remove a reference to Node B.

However from Node B type I'm only able to add a reference to Node A type - I cannot delete that reference successfully. (Node B type shows the reference removed, but Node A continues to show the referenced node B.)

I have tried using multiple widget types with both "unlimited" and "single" and can't seem to resolve this.