By the way, the excerpt above is from:
http://statutes.agc.gov.sg/non_version/cgi-bin/cgi_getdata.pl?actno=2007-ACT-33-N&doctitle=PASSPORTS+ACT+2007%0A&date=latest&method=part&sl=1&segid=1179820934-001856
My friend told me that one of his friend wanted to give up his Sg citizenship so can withdraw his very substancial CPF savings.
But the immigration officer tried all his might to persuade him to keep the citizenship so that he wont have to take out the CPF $$$. The officer also say they will "close" one eye to his unofficial dual citizen status...