As outlined in Security Bulletin MS14-025, Microsoft acknowledges the way credentials had been stored in the group policy field "CPassword" is insecure and is not to be trusted any more.
However according to their own Developer Documentation, they themselves had published the 32-byte AES encryption key well before 2014, allowing anyone chancing upon an encrypted ADGP password to decrypt it. I've seen articles speculate this had been published on MSDN sometime pre-2012, the earliest source I can find is 2013
I can't think of any good reason to publish this key, was this intentional or a mistake on Microsoft's part? Is this an example of an accepted public-secret where anyone operating a Windows server is allowed to reverse engineer this value from memory?