Mark,
It's likely the width of the Like button that you're using. In the content plugin, change it's width (I think it defaults to 250) to something like 100. Even though, in your picture, it looks like it can easily fit, since it's in an iFrame, the extra width is reserved for the widget anyways and the browser's automatically bringing it down to the next line... I think
Let us know, and thanks for compliments on 4.0. We're excited to finally get it out, and already planning 4.1
Alex