Hangouts History Mess

So I just noticed a weird issue with Google Hangouts history, and after some quick research online, I can't find a single mention of it anywhere.

In Hangouts, you have an option to turn chat history off. So lets click that button. It will give you a confirmation that history is off. Now you can type, send pictures, do whatever, and your history is off. Now lets say we're done with that, and we want to delete all that stuff that you just sent without deleting the stuff that is actually in your history.

You can't.

That's right, you can't. You can archive your hangout, but the second you reopen it, your "off the record" stuff is right back where you left it. You're only option to remove it for good is to delete the entire Hangout, which will permanently delete everything in it. Not to mention, deletion is only good for your end of the Hangout. The other person has to delete the Hangout on their end in order for it to be gone forever.

TL;DR: Don't plan a birthday party in Hangouts.