Uncaught TypeError: Cannot read property 'nTr' of undefined - fnGetPosition() with TH elements

Hi Allan,

Great job with the plugin, I can see a lot of work has been put into it!

I have noticed that fnGetPosition() generates the following error when used on a TH:
Uncaught TypeError: Cannot read property 'nTr' of undefined jquery.dataTables.nightly.js:4661

Here's the live example (same as example in documentation except with '#example th' selector):
http://live.datatables.net/egubir/edit

As I understand it, TH elements are allowed?

Thanks in advance,
Elan