Strange layout visible when I click on a post if logged as administrator

Hello again.

I find this product very good, but I still encounter an issue when I click on a subject once logged in as administrator.
Indeed the layout is strange.

Here is what I get if just a registered user (maverick see PM) :

Here is what I get if admin :

I get this code :

Erreur: 0 Error decoding JSON data: Control character error, possibly incorrectly encoded

 Where can I do something for that ?

Thanks a lot for your help.