This new feature where you can add notes to a flight isn’t working properly. I’ve added the reg’s to a few interesting flights I’ve heard but instead of applying it to just that one flight, it’s applying the notes to every flight with the same callsign.
You should be presented with two options
“Add a Remark for this aircraft (COA1448)”
“Add a Remark for this flight (KIAH-KFLL)”
(for example)
You should chose “this flight” if your remark is specific to that leg. Pick the first one (this aircraft) if it’s specific to the ident.
We should clarify the wording; clearly it was written with registrations in mind.
I did do that but it still doesn’t work. It shows that note for every flight under the same callsign.
To illustrate, I added the note under this flight :
flightaware.com/live/flight/CLX7 … /KLAX/ELLX
But the note is also showing for
flightaware.com/live/flight/CLX7 … /KSEA/ELLX
and every entry here
flightaware.com/live/flight/CLX775/history
Therefore I deduce that your feature is broken! 
Ah! Disregard that above now. I’ve just re-read what you’ve put and see what you mean. Clearly my interpretation of the options was wrong. I see I do indeed need to select “this flight” now for the info just to show for that one specific flight.