Select All Selects Too Much

I have a list form that is used to assign orders to shipments.

I filter my table data (the orders) and then write the valid records to a temporary table (gtmpTMSubprobill) and then I launch the list form using

FORM.RUNMODAL(37005447,gtmpTMSubprobill);

The list then allows the user to select some or all of the records and to assign them to a shipment with the push of a button.

The problem is that if the user clicks CTRL+A to select all and then pushes the button, it assigns orders that are not on the list and which (in some cases) are already assigned to other shipments.

Those records were filtered out before the form was launched. What is "Select All" selecting? I'm stumped.