XF 1.1 Weird overlay message after code button click

[Luxus]

Today I noticed that I get this when clicking at the code button:



I don't recall ever editing the editor besides very basic CSS adjustments to achieve a colour change. I doubt that CSS edits could cause the message above. Any ideas how to get rid of this?

 

[Onimua]

http://xenforo.com/community/threads/possible-javascript-error.32913/#post-376091