Bitcoin-QT: an address book label is overwritten or deleted when a Bitcoin address is opened by clicking on a Bitcoin URI #3814

Steps to reproduce:

• A Bitcoin address is in your address book and it has an associated label.
• You click on a Bitcoin URI referencing that address (such as "bitcoin:<address>?amount=<amount>").
• The URI is opened by the Bitcoin-QT client and the payment form is filled in using the specified address and amount.
• The Label field in the payment form is populated from the URI; if no label is specified in the URI, the field is left empty.
• After making the payment, the address label in your address book is overwritten (if the URI contained a label) or deleted (if the URI contained no label).

Fix:

• When opening a Bitcoin URI, if the referenced address is already present in the address book, don't overwrite or delete it.

Note: This happens both for labeled addresses in the address book and for labeled receiving addresses.

I suppose it could warn if an different label already exists in the address book for the address to be paid to, and give a choice whether to overwrite it or keep it.

Note that it is discouraged to re-use addresses.

Addresses are usually not reused, but sometimes you want to keep track of them (f.e. if an address is associated with a specific person, web site or business); due to the iherent user-unfriendliness of random character strings, labels are the only way to do that. If a label can be deleted or overwritten, this feature becomes quite useless.

If a label is not specified in the URI (which is the most common case), an easy fix would be to automatically fill in the "Label" field in the payment form using the label in the address book, like it already happens already when manually filling in the payment address.

Fixed by #3855