Online pay now anomalies (contribution transfer to new contact)

In the last months sometimes we experienced anomalies when people used the Online Pay Now payment link functionality.

Mostly this functions perfectly redirecting our customers to a payment page where they can complete the payment for the pending contribution.

https://www.ourdomain.nl/civicrm/contribute/transact?reset=1&id=7&ccid=3887&cs=986e9c03ddf2b4b980a929a_1492524606_1440&cid=316

Sometimes (very rarely) this goes wrong and we end up with the following:

1. The payment completes ok
2. But it is not contributed to the contact the contribution belongs to.
3. Instead a new contact is created
4. And the contribution is moved to this new contact
5. This new contact has the name "1"

I am not sure what goes wrong here, but I would think some more error handling would be required. Maybe the initial screen should show an error when the cid (= contact id) and ccid (contribution id) do not match?

I will try some more to replicate, but we had this several times in the last months. BTW. I do not have enough coding skills but thought this would be important as this seems like a data integrity issue kind of thing.