I've just done a test and there may be a "fix" for now - 

If you buy the postage label directly on eBay, the tracking information WILL update - almost immediately after it has been dropped off or collected. However, if you organise your postage elsewhere and enter your own tracking information (as seems to be the case with all users so far) then the tracking information will NOT update at all.

In my own case, I was using Royal Mail Click & Drop which did NOT get tracking updates. This is likely the case for any tracking number that you would have to enter manually, even postage paid for at a Post Office counter.

Granted, many business sellers will have their own arrangements and will not be able to buy postage on eBay. For many this will be far more expensive, as they will likely have business accounts with Royal Mail at reduced rates.

Hopefully this helps at least some of you, until eBay can be bothered to sort this out.