Adding rows to data --> filter not adjusting

Hello,

Everyday, I need to add rows to a pivot table and I actualize the pivot afterwards.
Some of my rows are not to be taken into account so I filter my data on one field. Let's say the filed is called "Stock quantity". I put this field in the filter-section of my pivot table and I deselect all the negative values of the field.
When I add rows to the datatable, and there are negative values in the "Stock quantity" field, I need te desect those again, but I noted today that those values are put at the end of the dropdown list while before the values where ordered automatically.
Therefore, I have to go throught the whole list looking for negative values, which take a lot of time if I have more than 100.000 rows.

Does anyone know how to avoid that problem or have to dropdown list to sort the values correctly?

Thanks a lot!