It seems that when I have a table inside a div and I set the table to 100% width and give it some margin, it seems to disregard the rightside margin. Here is the fiddle for it:
The width applies to the actual content of the element, so you have a table with 100% wide content, and on top of that you add some margins pushing the width over 100%, thus the right side of the table extends beyond the parent's right edge. Probably you should go with padding on the parent instead of margin on the table, or an additional wrapper <div> with just the margin.