Maximum Subletting Period
The maximum subletting period allowed is three years per application or as indicated in the approval letter, whichever is shorter. However, for subletting involving non-citizen subtenants (excluding Malaysians), the period of subletting per application is 1.5 years or as indicated in the approval letter, whichever is shorter. Non-citizens refer to Singapore Permanent Residents and foreigners. You are required to apply each time you sublet your flats or when you renew the subletting tenancy.

Eligibility Conditions : Subtenants
Citizenship
Subtenants must be :
a. Singapore citizens; or
b. Singapore permanent residents; or
c. Non-citizens legally residing in Singapore who are holders of Employment Passes, S Passes, Work Permits*, Student Passes, Dependant Passes, or Long-Term Social Visit Passes. These passes must have a validity period of at least 6 months as at the date of subletting application.
*Construction workers who are Work Permit holders should be Malaysians.


这个是目前的规定，租给马国人以外的外国人包括PR，每一年半要renew一次approval.也没有说租客必须是公民，而且公民当租客还有更多限制的。

http://www.hdb.gov.sg/fi10/fi10323p.nsf/w/RentOpenMktRentOutWholeFlat?OpenDocument

另外那个贴的表述让我很迷茫，不是很明白楼主到底说的什么意思。也许是单独的CASE，这个得看到HDB原文的信才知道。