Translation, as I understand it:
He was able to enter "Saints of the Black Moon" in the text field and it accepted it as a deck name. However, it would not appear in his list of decks until he shortened its name. He's asking that, if this name is invalid for length or some other reason, it not accept it in the first place.
It is longer than 20 characters, spaces included. Somehow, the deck building section passed it as valid, and it wasn't until he tried to use it that there appeared to be a problem. Something seems to be wrong with the input field determining length.