If clicking away from a purchase order, or changing a filter, whilst products are selected in the "add selected products" section of the PO (but not yet added to the PO), a warning pop-up should display to ask the user if they are sure they wish to abandon the current selection.
The team have quite frequently accidentally clicked away from a Purchase Order whilst adding products to it, which has resulted in having to start the PO from scratch.

Applying filters before clicking the "Add Selected Products" button with any products selected, also clears the selection and loses those numbers so a warning would prevent this.