It's not a Mac feature, it's a browser feature, and all browsers tend to do this. Like the message says, you got to the page you're on via some kind of form submission (virtually all sites these days are database generated) and so if you want to go back, it may involve having to resubmit that form. It's giving you a chance to think twice about this action, because maybe you just bought something on Amazon, and don't really need to make a second purchase of the same order.
How you managed to never run into this before is a bit of mystery unless this is your first computer or you previously were using a truly antiquated browser like IE6. So, the moral of the story is that however annoying this message might be to see, it'd be far more annoying to deal with some of the potential consequences. However, if you didn't just purchase something online or maybe update profile info on some site, then it's probably pretty safe to hit submit. Just make sure you're a little mindful of where you are from now on.
Often times (about one in five), when I try to revert back to the page I was previously viewing, I get a pop-up message saying "Are you sure you want to send this form again? To reopen this page Safari must resend a form. This might result in duplicate purchases, comments or other actions."
And the choice is either Cancel or Send. If I click Cancel, I cannot get back to my previous page unless I x-out the Web location I'm on and start all over again. If I click Send, it allows me to return to my previous page with no problem. But I'm afraid to click Send, because the consequences sound kind of scary.
Is anyone else a victim of this goofy, highly annoying Mac feature? And how can I make it stop doing that? Or can I?
Thanks in advance for comments, responses, suggestions, etc.