Mun Sen acknowledges that his uncle Boon Jin 文錦 gave him his first painting kit that was improted from England. Mun Sen returned to Sarawak and was the heir to the family's coconut estate, much to the resentment of his uncles who ran the estate. In the 1955 Poay Cheng Building School Fund catalogue, it is mentioned that Mun Sen and his uncle went to court over a dispute concerning the property left behind by his grandfather. Though awarded a thousand dollars by the court, he felt that his life was threatened, and decided to leave Sarawak for Singapore. He departed Sarawak first together with a few friends. His wife and children followed suit. The catalogue for his memorial exhibition in 1972 simply states that Mun Sen attributes his Singapore move to his realisation that he preferred painting coconut trees than to run the estate.

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1972. Pameran Peringatan Yong Mun Sen/ Yong Mun Sen Memorial Exhibition. Exhibition catalogue 17 March - 4 April. Kuala Lumpur: Balai Seni Lukis Negara/National Art Gallery; 金戈 Jing Ge，1955。’楊曼生傳 (Biography of Yong Mun Sen)‘ Poay Cheng Building School Fund Exhibition Catalogue, 4; 楊曼生先生從藝四十年. 南洋商报, 3 August 1953, Page 10