Just had a panic seeing one of my posts in TIO - it said "He's making you happy" and I was mortified because it was supposed to be "he's not making you happy." I thought I'd made a typo on my phone (on my laptop now - latest firefox on Windows 8). Clicked on it and was relieved to find out that I had included the not.
Went back to TIO and the not was gone again.
Out of curiosity, I refreshed the TIO page and the not appeared again. Then disappeared.
Tried a few times and noticed that the not vanished each time the video loaded, on the right.