Two plan with same acymailing list problem

Hello,

the following problem happen:

Plan A: when active it assing "User Group A" to user, and assing "acymail list A" to user.
Plan B: the same: when active it assing "User Group A" to user, and assing "acymail list A" to user.

When Plan A expires (it expires before Plan B): "User group" remain assigned to user (right). "Acymailing list A" is removed from the user (wrong).

Is it a bug or normal behaviour of Acymailing app?

Thanks,
Mario