I am unable to reproduce this behaviour on my own computer connected to the customer's database. So I don't think it's a plugin problem...
When entering serials for a GRN, they normally use a scanner, and so have it set to "next line on enter" on the serial # field. But they can reproduce it on a system without a scanner, using just a keyboard.
They open the serial form, enter one serial number and push enter, so that the cursor is on the second 'new item' row of the grid. They click on OK, and it magically adds a blank serial number.
If they save the GRN, there is a RE_LineDetails record with a blank SerialNo.
I figured out that the new row gets added as the button is depressed, so if you move your mouse cursor off the OK button prior to letting go of the mouse button, you can see the new row in the serial form. If you delete this 'phantom' row, and click OK, you get the right result ( a single serial # returned to the GRN form).
You can also re-open the dialog and delete any blank serials, and it works fine.
So the problem only seems to occur when they first go into the dialog.
This is doing my head in, so any ideas would be much appreciated.
P.S. you can 'sort-of' mimic the behaviour if you press the space bar in the second line. But then you will have an RE_LineDetails record with a single space for the serial #, not a blank one.