The top image here shows my pref setting, but, as per the bottom image, it doesn't seem to be sticking.

Am I misunderstanding the pref or experiencing a bug?

This is relatively new, but I haven't upgraded to Safari 13, so it began in some incarnation of Safari 12.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire