Raphael and Bootstrap layout

[vrmerlin]

I'm trying to place two Raphael diagrams into a very basic bootstrap layout, but it's not behaving properly.

Here is the plunker: http://plnkr.co/edit/p3k99ngacdQbUN7m5Df7?p=preview

If you make the result area wide enough, you'll see the "Right Side" column sits on top of the Raphael diagram, even though it's in a different bootstrap column. If I replace the "span" Raphael tags with simple text, the layout works fine.

Is this a bug, or am I doing something wrong?