This sounds like someone doesn't understand how Windows calculates folder sizes. It will never show the size unless you look at the folder properties; and even then, there's no indication when it's done calculating. It might be obvious sometimes because the number is continuously changing, but if it hits a lot of very small files, it won't visibly change for a while.

Edit: Actually, apparently there is a bug related to this in recent versions of Windows, but it's still a behavior that can happen even without a bug.

Ah. Though that's still opening the properties dialog, which is much rarer than browsing.

Also they're reporting that it only happens with full filenames over MAX_PATH, so it's a very different bug. The base idea of "show a continuously-increasing size until don't calculating" works fine