I haven't tested it, and don't plan to.
But it may be similar to shifting into reverse.
If vehicle speed is >7 mph, shifting into reverse causes the vehicle to go into neutral very fast.
But if vehicle speed is 7 mph or less, the vehicle will engage reverse, and as Stoaty reported in another thread, the LEAF will come to a very abrupt stop.
That is probably NOT very good for the car, and if someone is following you closely they'll probably hit you.
Putting vehicle into Park at >7 mph, LEAF will just give you the chime warning.
7 mph or less, I'm not sure what it will do, but there is a chance it will stop abruptly.
Hopefully it won't try to engage the mechanical parking pawl in the transmission before it comes to zero speed, because if it doesn't, that will be very bad.
LEAF parts are very expensive, so I don't plan to intentionally test it.
I did unintentionally one day hit P while the vehicle was still rolling very slowly backwards, probably slower than 1 foot in ten seconds.
The LEAF came to a very abrupt stop with a slight chirp of the tires. Not good, and I plan to avoid doing that again.