

It's probably an unintentional result of the way the tree was built rather than a fact.
Multiple ways to deal with it but probably easiest for you would be to attach a profile to Simon as his mother then merge it into the existing profile of Joseph's mother.
Alternatively, in Tree View, use the CTRL button to toggle Move Mode then drag Simon's name card on top of the name card of Joseph's mother then follow the onscreen prompts to set their relationship.