Lot-serial numbers

After solving PDF problems with the new version 13 I see that there is ability to delete or to repair the products that add with serial number etc. Trying to repair and delete one of them I received the error that this product exists with different day of 1-1-1970 that you try to repair or delete reltively.
I went in dispatch.php line 462:
$eatby = $supplierorderdispatch->fk_product;
and I replaced it with the more reasonable
$eatby = $supplierorderdispatch->eatby
and repair is working (not as i would like but it works)
I went furthermore at line 409
and I replaced accordingly:
$eatby = $supplierorderdispatch->eatby
Now both delete and repair of poduct with lot/serial number are ok.