What does "never for this site" for the canvas warning really mean?

When I get an html5 canvas warning in Tor Browser, it suggests that I pick "never for this site".

To me, the word "never" implies that Tor Browser is writing down my answer, and it will use that answer forever after. Like the "permanent exceptions" for SSL certs.

On the other hand, my understanding of Tor Browser behavior is that it wouldn't write it to disk, so my choice would be lost on the next browser reset or new identity click.

There's a contradiction here. I'm assuming the second one is right. Is there a better phrase we can use than "never"?