Hi @woolly, thanks for reporting this.
I've looked into it and it's definitely a thing. However at this time it behaves exactly the same as in Safari when Option is held. Please see the following recording:
Moreover, when Shift is held - it animates much slower than usual.
Safari might improve or fix that WebKit behavior in future, or even we might find some solution for that.
However I'm going to mark as NoFix for now, since there's not much we can do about it at the moment.