Timebox cannot auto-change the hour by pressing the arrow icon in zh_TW locale (IE and Webkit only)

For example,

<timebox id="tb2" cols="30" format="long" locale="zh_TW"/>

1. Please put the cursor in the hour area, and keep pressing the UP/DOWN arrow
2. The cursor will jump to the 上午/下午(AM/PM) area (that is a bug)

What's the expected result?
1. The cursor should stay on the hour area.