Random ads.. all equals

Hi,
first of all.. great plugin!

I have a strange issue: in section “Random adverts” I created 10 ads (10% ratio each)

I set up to show 3 random ads in every single post.

Result: I show 3 text ad in my post.. but they’re all equals:
if I refresh page i got another ads repeated 3 times in the page

url: http://www.isocial.it (test in single post, look at link ads, not banner)

thanks for your help

(actually i’m also testing an head ad)

https://wordpress.org/plugins/ad-injection/