I'm doing a bunch of scripting in Node.js with the API, and I'm hitting a strange edge case where sometimes a fresh session key isn't considered valid for some operations, but goes through fine for others. I'm setting the key in the header, and the /add_tags/get_tag_services will say it's not a valid access key. I assume it hasn't been updated to be aware of session keys. It's not a huge deal, just something that tripped me up that I wanted to mention.