It would seems pretty lame if Singapore govt don't give him back the citizenship. His case was just forgetfulness, not that he obtain citizenship else where.
http://news.asiaone.com/News/The+New+Paper/Story/A1Story20090104-112246.html
WAYS YOU COULD LOSE YOUR CITIZENSHIP
1 Those who hide past criminal records when applying for citizenship.
2 Someone who is considered to be a security threat.
3 Those whose birth or citizenship status was not registered by their parents or guardians.
4 A child born to a parent or parents who are foreigners and not legally married at the time.
5 A person born in Singapore who uses travel documents under a different nationality.
6 A person whose citizenship the government cannot establish from its database, and who has no documents to prove it.