Copy issue in Pages

I have a really weird issue with pages that sometimes the copy command (like for example copying the text) doesn't work for me. I can see that by copying a text in pages and trying to paste it back again -> nothing appears by that..
This problem appears only in the program pages and nothing else. My OS X or pages installation is not the problem because I already reinstalled both and the problem is still appearing right now.

Has anyone a clue how to fix that ?

 

Newest OSX + newest version of pages.