There are a lot of URLs out there on the Web; and a pretty big number of those URLs are either alternative names for something, or old locations that have been superseded. So “redirects” from one URL to another are a common feature of the web, and have been for many years. But recently, the way these redirects behave has been changing, because performance-conscious browser developers have started caching redirects, rather than re-requesting them from the server every time.
In theory, this makes perfect sense, but in practice, it causes web developers like me a lot of pain, because nothing “permanent” is actually that permanent. I’m not saying no browser should ever cache a redirect, but I do have a few suggestions of ways they could be a little more helpful about it.