Just an hour ago I had the similar problem except the problem occurred when I had specified overflow's value as auto. I didn't use overflow-x or overflow-y, I just needed it to fully contain my two lists that were floating on opposite ends.
What worked for me was that I changed overflow's value to hidden. Try that. I had set the max-width to 100% and instead of specifying height, I just used overflow: hidden.
Hope that helps.
