The multiple sharing option has gone away! How to fix it?

Hi, everybody.

Some months ago, I could use multiple sharing option when I click on the arrow beside the button "Share". There would be a line "allow multiple sharing...". But now, when I lick on it, just a window appears without this function - multiple sharing simultaneously. Could someone tell me why and how to fix it? Thanks.

(picture of losing function - multiple sharing)

Minh.