A donor reported, and I was able to replicate, a bug on the donation form. They entered their donation amount and clicked card, and on the following window entered name, address, email and card #. They then changed their email address to a different one, but after pressing donate the TY email came to the first email address they'd entered.
The form does not let one modify the email address after entering a card #, though it appears to. This is not a gigantic problem so I'll set priority to normal, but it may generate donor confusion, bulk email complaints, or unnecessary requests for donation receipts and would be cool to fix.
The donor who encountered this is cid=26630106, and my test donation where I replicated this was GLOBALCOLLECT 906157881, via Firefox 61.0.2 and donate.wikimedia.org