Why can buyers still leave feedback after cancelling a purchase?

[ntomntom]

Recently sold an item on ebay and issued an invoice.  I had no contact from the buyer after 3 days so sent a message (politely) asking if they intended to pay.  They replied saying circumstances had changed and they didnt want it any more -it was just before Christmas so I guess they found an alternate present!!  So I cancelled the transaction to get my seller fee refunded.

I then had negative feedback from the buyer saying I was "unhelpful" in the comment.  

Now I have successfully appealed this, so full marks to ebay for that, but why should buyers be able to leave feedback if they request a cancellation?

It would appear I can bid on anything I like.  Change my mind and not pay.  Then leave negative feedback for the seller.  I can see no valid reason to allow feedback to be left in these circumstances.  If I refuse to pay, why should I be able to leave feedback?

EDIT:

To be clear, I have just checked & actually I did open an Unpaid item case (rather than cancellation).  And it has been settled.

My issue is the fact that the buyer was then able to leave negative feedback.

Why would the system be designed in this way?  Credit to ebay the negative feedback was removed when I raised it, but why should I have to spend time chasing this when the system should not have enabled the buyer to leave feedback under these circumstances.

[john1297576]

Completing an unpaid case only prevents Feedback being Left after the case is closed. Your buyer must have left a negative before you closed the case, so you had to ask for removal.

At least I have learnt something, as the impression is given that removal would be automatic, but using the Seller Help a request for removal is fairly simple.