Checkout Step 3 - Header goes crazy

So I've modified my header code but none of the checkout code - the header works perfectly for the whole site until you get to step three of the checkout process, then it goes really odd and the dropdown menu falls below step three.

Is there any logical reason for this? As the header is fine everywhere else, and on every other step I don't think that it is my header code.

Any help is much appreciated.

You probably have use a css class that is used in the checkout within your header.

Thanks, I'll check this out when I come back to it and update the thread accordingly.

So I tried looking to see if there's any clash with the css - there isn't and strangely, if I refresh the page at the stage it messes up, the page reloads correctly :S any ideas?

I ended up re creating my header using only the original CSS with a few overrides and managed to get it working OK… for now.