Stress can make you forget stuff like that. There is nothing wrong with it, and It doesn't mean that Wanko loves Sakuma less or anything. It does suck, though.
@GoggledAnon by my understanding, the most common way to type Japanese uses a standard English keyboard layout that basically gets turned into Japanese characters using auto-correct. Based on that, I suspect the "tp" at the end was supposed to be a typo of "to" which would make the ending become "お目出度". The "b" in the middle could be a similar typo, intended to be "bi" to complete "誕生日", though it could have been an intentional pun instead.