Of course not. I hired 2 bun bun before they worked in Singapore for Chinese employer. They can understand & speak some Mandarin. After they came to my home, they can understand Cantonese very quick even speak some Cantonese with my children. Even my 3 previous bun bun with Taiwan working experience, they are the same case. Now I hv a Indo works in my home for just 5 months. She worked in Singapore 1 year ago for Chinese employer. Her cantonese is in Mandarin style (i.e. 很多, 沒有呀....). She even sometimes speak single work in Mandarin. Even she cannot speak very well in Cantonese, she is improving under my pushing.