Who has stolen Clarabelle's " mummy" ?

Whenever Clara pester me to carry her, I'll always take this opportunity to make her call mummy. What puzzle me is instead of calling me mummy which she already can, she always call me " daddy ". I thought she might need some recap " Im not daddy, Im your mummy, call ma-mi " but still " daddy " spill out from her mouth. I try to inspire her with her favourite hand-kiss action and mm..ma sound but still she refuse to say mummy and start her "Ah bi, Ah bi" (whenever she is angry she always say " Ah bi ").
This morning I got another good chance when offering this hungry little girl milk. I make her call "mummy" first before giving her the milk. Still the same, she called me "daddy". I tried very hard refreshing her "ma-mi" with emphasized lip but she seem very impatient and hungry and finally she said " barney "! ! ! As I wouldnt wish to starve her further, she has her reward and leaving me with a perplexing question ? ? ?