Robert Harvey's answer to What is the average number of tags per question in Stack Overflow and Stack Exchange as a whole? inspired me to go looking. On SO there are 24 questions with more than 5 tags spread out from 2008 to mid January 2011, see this data query.
I couldn't be bothered to check every site but went through about 10. The only other example I found is here, this question actually, which is from November 2011.
How is this possible? Is it still possible?
P.S. I'm not asking whether it'd be a good thing.
and I couldn't replicate it when creating this question.