Unable to select multiple item tracking lines


My client is on version 3.7. There is an issue in selecting multiple item tracking lines:

When we try to select multiple item tracking lines from the Sales Order - Item Tracking Lines screen (by clicking on the asssitedit button at the ‘Serial No.’ field), only the last selection in the Item Tracking Summary screen is getting copied onto the Item Tracking Lines screen.

Why is this happening? I got no clue looking at the OnAssitEdit() trigger on the ‘Serial No.’ field.

I was told that we can use SETSELECTIONFILTER for this purpose. Any clues as to how the multiple selection of the item tracking lines can be done using SETSELECTIONFILTER?

My client insists on having this functionality in place. Please help…