Drop-Down Error on Subform w/ Mobile

Drop-Down Error on Subform w/ Mobile

I have an equipment leasing app.  The main order form is the order "header" information (customer name, address, phone, etc.).  A subform is used to record the individual items on the order.

Two pieces of information are entered for each item leased - the item and the serial number of the specific unit that was leased.  The application has a table with the serial numbers of each item (a child relationship to the parent of items).  On entry of a lease, 

1.  The user selects the item from a drop-down on the subform

2.  The serial number drop-down displays the serial numbers for the selected item and the user selects the serial number of the item being issued.  

The serial number field is a look-up against the unique serial numbers form filtered by the item being leased.

It works fine on a PC.  However, on the mobile app the serial number drop-down does not display the serial numbers.  Instead, it consistently displays one item with a serial number of 123, and none of my items have a serial number of 123.

Anybody have any ideas on why this is happening and what could be done about it?

Thanks,
Jon