This was what I heard while working from one of my colleague who
is going to get her PR soon. She mentioned that if you renounced
your Malaysian citizenship, you can only stay in Malaysia for at
most 14 days at one go instead of 1 month for those who were
originally SIngaporean.
I can ask my father if you want to know more, he used to be
Malaysian and then got his PR after which he converted to become
Singaporean without going through NS cos he got his PR quite late
if I'm not wrong (saw a certificate from SAF or something like that
saying that he is not required to serve NS which was issued in 1990
when he was already 33 years old).