It is a bug in ecart that it is using the wrong code.
the correct code for this line:
$Shipping_PackageArray[$Shipping_PackageIndex]["WeightUnits"] = "".strtoupper($eCart1->WeightUnits)."S" ."";
is:
$Shipping_PackageArray[$Shipping_PackageIndex]["WeightUnits"] = "".strtoupper($eCart1->WeightSuffix)."S" ."";