@Kaarme
I'm just guessing here, since I don't read the raws, but the "master" that maids in maid cafés usually use, is ご主人様 (goshujin sama), which can mean "Lord" or even "husband". It implies someone in charge.
The "master" you're referring to, is the one that implies mastery of some kind. The Japanese use different words for them.
[ul][*]名人 (meijin): expert
巨匠 (kyoshou): maestro
達人 (tatsujin): expert
玄人 (kurouto): expert, professional, connoisseur, prostitute
マスター (masutaa): owner, leader, master (of a skill), master device, master recording
[/ul]
... but goshujin sama is not one of them.