The model sale.order have order lines (sale.order.line) that can be created/edited directly in the tree view by adding the attribute editable to the tree field. Their relationship is a One2many.

I can't make this work for a custom model I'm working on with a Many2many releationship to the field I want to create/edit. When I click create or edit an item it pops up in a seperate window istead of "inline" or directly in the tree view.

Is this possible?