Spinner with <input type="number"> produces double set of arrows under Safari & Chrome

Spinner with <input type="number"> produces double set of arrows under Safari & Chrome

I have used the jQueryUI spinner example to show that adding 'type="number"' causes a double set of up/down arrows to be displayed in Safari 6.0.2 and Chrome running under Mac OSX 10.7.5. There seems to be not only the jQueryUI set of arrows but also a native set of arrows. No problem with Firefox.

Is this a bug, or have I done something wrong?

website for the example