Sorry for the ress, but I solve this in Persona with HTML and CSS, just declarating the Sidebar widget-area in categories.tpl and CSS to fix the categories width.
I'm newbie with front-end, but this "fix" is functional atm.
@baris Guess that should have been the obvious, and yeah, we had some code that would auto generate a background for users. Disabling that did fix it. I really appreciate the help, feel kind of stupid now lol. Besides that being fixed now we still have an ongoing issue with plugins not working like emoji's, shoutbox, and so on. And words of advice on that?