Strange behavior with MAToManyRelationDescription

Hello all, I am building a form that consists of two components, e.g. House and Person. For each of these, when a new one is created I register it. I have a manager class that displays these using: MAToManyRelationDescription new classes: (Array with: House); label: 'Houses'; accessor: (MASelectorAccessor new readSelector: #houses; writeSelector: nil; yourself); default: Array new; priority: 20; yourself People is similar. The Manager class is a form, but with no buttons as it is only needed to let the add buttons work on these relation descriptions. The accessor shown here, houses just calls "House instances" to get currently registered houses. I subclass MACheckedMemento and create a custom memento that simply overrides the #push: method to see if the object is new (no members will be set) and if so, registers the object after called "super push:". Everything is fine except for Houses, after I create a new hause the main display always shows 2. If I leave the page and visit new I see only one. I have looked around but I dont see how this is happening. Any ideas?