Margins don't collapse/combine?

Hi guys, I have a container with components in them and have margins set for the components. The components margins seem to add on top of eachother intead of collapsing.

For instance, if I have a container with bottom margin of 10px and a container below that with a top margin of 15px, the combined distance between the two containers is 25px's. Normal CSS dictates that only the largest margin should be used (in this case 15px).

What's going on?

Margins don't collapse/combine?