Two Select Fields Changing each others values

When I load my form and select a customer this changes two select fields to only show items associated with that specific customer

Serial Number automatic lookup
SELECT hardwareID, serialNumber, customerID
FROM hardware
Where customerID ={customerID}
ORDER BY serialNumber

Asset Tag Automatic look up
SELECT hardwareID, assetTag, customerID
FROM hardware
Where customerID ={customerID}
ORDER BY assetTag

When I select an asset tag from the list it updates the Serial number field with the proper serial number
However when I select the serial number it does not update the asset tag field.

Ajax on change event for Serial Number Field
$check_sql = “SELECT hardwareID, typeDesc, hwModelDesc, vendorname, warrantyEndDate, assetTag "
. " FROM hwalldet”
. " WHERE hardwareID = ‘" . {hardwareID} . "’";
sc_lookup(rs, $check_sql);

if (isset({rs[0][0]})) // Row found
{
{hwType} = {rs[0][1]};
{hwModel} = {rs[0][2]};
{vendor} = {rs[0][3]};
{warrantyEnd} = {rs[0][4]};
{assetTag} = {rs[0][5]};

}

Ajax onChange Event for Asset tag field
$check_sql = “SELECT hardwareID, serialNumber, typeDesc, hwModelDesc, vendorname, warrantyEndDate, assetTag "
. " FROM hwalldet”
. " WHERE hardwareID = ‘" . {assetTag} . "’";
sc_lookup(rs, $check_sql);

if (isset({rs[0][0]})) // Row found
{
{hardwareID} = {rs[0][0]};
{serial} = {rs[0][1]};
{hwType} = {rs[0][2]};
{hwModel} = {rs[0][3]};
{vendor} = {rs[0][4]};
{warrantyEnd} = {rs[0][5]};

}

I feel I am missing something simple but I just cannot seem to figure it out.