I posted a question about MD5 hash collision back in 2014. As far as I know questions about algorithms are on-topic on Stack Overflow, and the cryptography tag did not have the warning "CRYPTOGRAPHY MUST BE PROGRAMMING RELATED" back then.

Someone reported it for being off-topic, but a mod declined it with a comment "I see no reason why this is off-topic. Not a programming question? You must surely be joking!", so it seems that this is controversial for the mods as well.