orderby=rand shortcode not working

I have been using this combo of shortcakes [jobs per_page=”21″?show_pagination=true orderby=”rand”] and it’s displaying results in a strange way.

Reloading the page changes the order of listings, so there is some randomness involved. However, the same 21 listings are always on page 1 and again the same 4 listings are always on page 2. Is that normal behaviour?

As well, there are some listings which are missing, and others which are duplicated on page 1 and 2. So the total number is correct, but the listings themselves aren’t. When I delete the orderby instructions, then the listings display correctly, 25 unique listings on 2 pages.

I am using the Robolist Pro theme, in case there are known issues with the theme.