When I saw this I just could not accept it so I looked into it. Some box's contents is pre-determined and some is randomly selected but as you click the chest and not as you enter the house. The one you selected did indeed have an effect on what you got, even if it was just an identifier in the randomizing code.
Comments
I was lied to as well
Luckily that is wrong. Your childhood is safe:
http://nintendope.iodized.net/smb3/10.php
Credit to Reddit comments.
When I saw this I just could not accept it so I looked into it. Some box's contents is pre-determined and some is randomly selected but as you click the chest and not as you enter the house. The one you selected did indeed have an effect on what you got, even if it was just an identifier in the randomizing code.