why x-scrolling is not enabled?

Hi,

Check this (http://jsfiddle.net/royling/DCYPH/10/), why is the x-scrolling not enabled?
I've set the "sScrollX" as a very small value - 50px so that the table is obviously wider than that, but I didn't get the horizontal bar either...

Only if the "sScrollXInner" is set as 110%, the horizontal scroll bar shows. But in the document, it's saying this is only an optional parameter.

Any problem in the setting?

Thanks,
Roy