Steps to reproduce:
1) create payment;
2) go to payment's card;
3) add product or service;
4) set quantity of added product or service to >1 value;
5) choose action "Create closing document";
6) set kind of closing document to "Act";
7) press "Save";

Expected result: quantity of product and service at closing doc's card will be equal to quantity at basis payment card's
Actual result: quantity will be equal to 1.