Apologies in advance if this was ever answered, but I started getting a headache around page 15. I think I'm having this same problem. In the admin panel, in Configuration -> My Store, I set a $5 welcome voucher. Tonight I got an e-mail from a customer that said:
"I'm a new member here at your store and believe it somehow just gave me a $5 voucher I don't think I was suppose to get.
I'd already used my new member one but when I made my second purchase here it again discounted the price 5 bucks as well as still more importantly showing I still have a $5 dollar voucher balance. So anyways to keep this brief I believe I owe you'll five dollars still and thought I'd best mention this happening to me while shopping here."
I haven't had any other problems with the contribution. Everything else works great, and is totally appreciated. Any ideas on why it doesn't want to cancel out the welcome voucher after it's been used? I don't see anywhere in the admin panel to edit it like you can with a regular voucher other than to edit the price.