Script preview Problem

Hi Experts,

I'm going through T-code MB90.How its related to z print program i don't know.By entering the value in the selection screen for mb90 t-code i'm going to another screen there i'm clicking on one check box & clicking on print priview & able to see print priview page.

When comming back once by clicking back button & selecting once again check box & clicking on print priview button ..its showing wrong item line & no of pages are more than before.

Pls suggest.

Thanks.

Singha