I have two Concrete5 websites, both of them gradually became more and more difficult to edit due to the dashboard and any other editing window graphics screwed up. After some investigation work I discovered the cause is Google's new 'Page Speed Optimization' feature that I had enabled in my web-hosts control panel. Once this is turned off Concrete 5 performs very well with no trashed graphics. I should mention that it was only on the editing side this happened. The public facing side was unaffected. Hope this helps anyone with the same problem.