Columns changing

I have found that the first block will start in the right hand column, and then change to full width when I have been scrolling through the page.

chainreaction . mathiaseverson . com

Any ideas on why it’s happening?

I see the issue. I’m guessing you mean in Firefox? It’s not happening in Chrome.
Add this please to the bottom of your style.css:

.entry-content {
   clear: both;