Displaying in wrong place on mobile

[callumacrae]

Expected:

Actual:

(displaying over content instead of below it, triangle missing)

This happens when loading the page on an iPhone, but it doesn't happen when you load the page on an iPad and change the width after it's loaded (which is what the first screenshot is actually of). That makes me think it's a problem with the library, because I'm styling it using CSS only!

Any ideas?