I like the hobbit presents, but I do not like accidentally spending my mithril coin on them. I have accidentally double clicked the button several times in the past. You end up with a free present, and one purchased for mithril coin. Those second clicks were mistakes, and I did not really intend to make a purchase.
The interface should not re-purpose the same button (screen location) from 'get a free present' to 'purchase a present'. The user should have to select a different looking button in a different screen position to make the transaction. Also, all mithril purchases should require verification from the user, that they actually intended to make that choice. Tonight my gold present did not become available for some reason. If I had not been paying close attention, I would have ended up spending mithril coins trying to pick up my free gold present, that for some reason the system did not offer this week. Making this change would prevent problems such as this, or double clicks, from causing undesirable actions for the customer.