Total check box in Screenset Results is not working for refnum values

Hi,

We have a requirement where in a customized order release screen set ,total of all values in a column should appear at the bottom for selected records. For this we have marked the "TOTAL" check box in screen set results. The problem is that this functionality is working for total gross weight or total gross volume but when we try to use this for adding some refnum values, it is not working. We are not sure if this is a bug or we are missing some setup.Please help.

Thanks

Shashank