Re: Code Plugin display issue
First, I think you may want to remove your screen shots. I think they include more than you expected (scroll to the right).
I can recreate your problem on TW12, but only when I select the same Theme as you have: "Thenews" and only when I also have "Syntax Highlighter (CodeMirror)" selected in the "Editing and Plugins", "General Settings" tab.
Maybe you could turn off the "Syntax Highlighter" option, or try a different Theme (Note: the problem is there in the Thenews for both the "Narrow_left_column" and "None" Theme options).
Tom