When I have two or more models in the model list (left upper), and have one or some selected, they all do print - even the unselected models. If that is intended behavior, I do not understand what the select/unselect box is for.
That is the intended behavior. That just hides the model, not real useful.
You need to open the process and on the bottom of the first tab is a button to select the model, all are selected by default, only select the models you want to print.