"I didn't say that!"

This one seems unrelated to what you say. I tried saying the exact same thing again, and it went through fine.

Seems to be some kind of buffering error, where the server swaps your message for something someone else said, at random.

I'm guessing the same thing can remove whole lines as well? I'm noticing in the 2nd SS that your 2nd line "You can CC blah blah" wasn't there.
I've yet to see this happen to anyone I know or to myself, so this is rather daunting.