It still sounds like PayPal doing a pre-authorisation check rather than it being anything to do with eBay; the "EBAYUK" part of the payment reference will be to tie it to the payment to eBay.

This used to be common with many debit card payments (not just via PayPal) as a debit card payment doesn't immediately go to the merchant. What actually happens is a "pre-authorisation hold" is placed on the buyer's funds; as far as the buyer is concerned the funds are immediately taken from their account but in reality the funds have been ringfenced by the pre-authorisation hold but remain in the buyer's account. The funds are sent to the merchant once an authorisation has been received at which point it takes 2 to 5 working days for the funds to actually clear into the merchants' account.

The whole point of obtaining a £1 pre-authorisation hold is to check the associated bank account actually has funds available; the actual authorisation is never sent for that payment so the £1 will appear back in the buyer's account once the pre-authorisation hold has fallen off it. 

It sounds like you are using PayPal as the payment method but a debit card linked to PayPal as the funding source rather than a PayPal balance - you would almost certainly be better protected if you used the debit card directly at checkout. Where "item not as described" claims are concerned PayPal only affords 30 days from the date of delivery to file a claim. You can usually file a chargeback with your bank up to 120 days following payment but you likely won't have that protection with PayPal (a digital wallet) involved. However, in this case it will only become an issue if eBay don't refund you under the terms of their Money Back Guarantee.