If you have a user with short username and name (like 3 letters), you can't search for them in Add Contact menu (it requires at least 5 letters to input). It throws a warning but still fills the username and name fields and you are able to add such user then. But that warning makes you feel it won't work. If it still works, why show the warning at all?
Spark now requires at least 2 letters (with less it timeouts and Smack throws an exception). It is more reasonable now than requiring 5 letters as before.