In accordance with the "One Country, Two Systems" policy, China made a special arrangement for the application in special administrative regions (SARs) of bilateral international agreements to which the People’ Republic of China is or becomes a party. The operation of this arrangement in the past 20 years has been largely smooth. Nevertheless it has met with occasional challenges, which culminated in the recent case of Sanum Investment Ltd vs. Laos People’s Democratic Republic. In this case, the Appeal Court of Singapore made a decision totally opposite to the institutional expectation of the special arrangement for Macao SAR. This paper argues that the Court misused some concepts and theories of international law, such as the Moving Treaty Frontier rule, Critical Date and Subsequent Agreement, and consequently came to the wrong conclusion. Nonetheless, as this case indicates, China should not take it for granted that other countries are as familiar with the treaty arrangement in SARs as China itself and should take necessary measures as soon as possible to solve this problem.