These sorts of problems are generally difficult to solve if you can't alter the HTML. The challenge is the design edit bars are added in client side and attached to the div structure that the system adds when including a component. Normally these sorts of problems occur when you have complex float based layouts, or negative margins. There is no simple answer other than trying debug the generate HTML/CSS and adjusting your CSS and markup. I have found that often the only workflow solution is to apply an author only CSS changes the layout for author mode, or changing the HTML markup when in author mode. Most of these solutions require cooperation with your CQ component developers to implement the author only solutions.