Yes, the problem is that iPhone’s HTML layout engine breaks the page when you rotate the phone, then breaks it further when you rotate it back to where you were. I put the viewport tag in to solve the iPhone, but then the iPad came out and there’s no way to have a different viewport for an iPhone / iPad. Blame Apple, I’m still trying to find a working solution.
Edit: indeed, this is a bug: there are different CSS styles for devices with < 480px screen width and > 480px (via @media CSS rules). Desktop browsers pick the latter style and ignore "viewport" meta tag. iPhone picks the former style and takes into account viewport. iPad picks the desktop style and takes into account viewport, which disables zoom (intended for the iPhone style version).
Now that I debugged the problem, can we instead report bugs to website designers instead of commenting here on HN?