How are you remixing it? There's the "Remix your own" button on the project page, and a Remix button in the menu if you "View Code" first. Both work okay for me.
Has your editor tab been open for a while? If so, the code may have changed. Make sure you refresh the browser and try again.
If that doesn't work, let me know what Browser/OS you're on, and we'll dig into it further.