Deleted branch keeps being shown in a list of branches assigned to a Moderating group

1. Go to User Groups, create a new User group.
2. Go to Forum Structure, create a new Branch, choose the User group, created on Step 1, as a Moderating group for the Branch. Save the Branch.
3. Delete the Branch.
4. Go to User Groups, select the User Group created on Step 1, press Delete.
Actual Result: the popup window "Are you sure want to delete the group" still shows the Branch from Step 2 in a list of branches assigned for this User Group.
Expected Result: The deleted Branch shouldn't be shown in a list of this Moderating Group's branches.