I think the person maybe wants it to list them as being married at the same time. Bob Smith is married to both Sarah Smith and Elizabeth Smith.
As it is right now you can have someone connected to unlimited people as a "partner" but the tree will only show them as having one current partner. In my example of Bob and his wife's Sarah and Elizabeth the tree would only list one as his wife the other would be reverted to ex-wife. Even though Bob is married to both of them and would prefer the tree list them both as being his spouses.