basic key binding not working as expected

[scriptspry]

Testcase:

https://jsfiddle.net/xf0sf6zg/

What I did:

keydown shift first, then keydown s

What happened:

"You pressed shift and s together." was logged twice!

What is expected:

That the message be logged just once.

Additional info:

The reverse is not true. keydown s, then keydown shift == message logged just once!!!