An identity with its membership which just expires proceed block calculation
Cf: https://forum.duniter.org/t/g1-test-dans-les-choux/4192/316?u=moul
It is not happening when launching pow with an already expired membership identity.
But, it happen, when an member identity is calculating, then loose its membership and keep calculate.
There is no further check at each block if the identity is still member. A mechanism should handle that.