I was hoping that only happened at few enough window sizes that not many people noticed. This is an unfortunate side-effect of using iframes to show inline examples. There are a few solutions - I'm hoping to have time to work through one of them this weekend.
I wasn't really looking for problems, it's just something I noticed very quickly. Bad luck then I guess. Upon further testing, it does only happen with certain window sizes indeed.
But it's a typical example why front end development with web technologies still isn't where it should it be.
And I'm not blaming the front end devs, the technology just isn't up to the task. The fact alone that you have to deal with problems like this is telling enough.