Google Play Games Plugin(A simple issue)

Hello,

I am using google play games plugin in this link. I have a little problem. Google play leaderboard is opened two or three times(or more) if i click on submit score button more than one time in a row. After i close first leaderboard, second one opens without i press button after i close second one, third one opens etc.. I was going to put a bool on leaderboard's back button but i couldn't find the place where back button of leaderboard, is called.

The think that i want to do, is activating leaderboard button after leaderboard is closed, to prevent this problem. What should i do?

Thanks.