I guess I should out myself as a Chromium HTTP stack maintainer (since 2009, so this behavior predates me). One might consider me a domain expert here. I participate in IETF HTTPbis for the HTTP/2 work as the primary Chromium representative. I am not involved with the RFC 2616 revision work as that's tough, thankless work, that thank god we have Julian Reschke and Roy Fielding working on. As far as I'm concerned, I owe them a drink everytime I see them. They do an awful lot of legwork talking to various implementations and trying to build consensus on actually conforming with the standard and all its edge cases. It's really quite unfortunate to see this blog post author treat them so unfairly, although I can see how one might easily jump to his conclusion.

Now, as far as "SHOULD NOT", that's a reasonable thought for people not aware of what popular user agents currently do. The thing is, the majority of major browsers rewrite POST to GET on a 301. Here's my browser's code for it: https://code.google.com/p/chromium/codesearch#chromium/src/n.... Here's Firefox's code for it: http://mxr.mozilla.org/mozilla-central/source/netwerk/protoc.... To my knowledge, all browsers implement this behavior. We basically copied IE's behavior, because, IE did it and websites expected all user agents to do what IE did. Story of the web, sound familiar? :P

So, as you can see, Julian was merely acknowledging the pragmatic reality of the situation when he updated the httpbis specs to reflect this behavior: http://trac.tools.ietf.org/wg/httpbis/trac/changeset/1428. And this reasoning behind it is covered in the introduction to the relevant section in the httpbis docs: http://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-2....

"SHOULD NOT" implies that our implementations are behaving badly. Now, it's true, our implementations may not be behaving ideally from a spec cleanliness point of view, but interop trumps spec cleanliness, at least from the perspective of anyone who actually deploys real software on the internet. So it's probably best for the spec to acknowledge this and officially allow this. Specs that don't mirror reality are...probably not just useless, but actively harmful.

I hope that explains things, cheers.