Experts believe that Vietnam's statement demanding the immediate recall of a special series of Chinese postage stamps from circulation has revealed Vietnam's double standard on territorial issues.

On Oct. 28, China Post issued stamps depicting five lighthouses constructed on five reefs of the Nansha Islands. On Dec. 14, Vietnam’s Ministry of Information and Communications said the stamps violated the country's sovereignty, urging China Post to respect Vietnam's history and decommission the stamps.

China started building the multi-functional lighthouses in 2015. The five structures provide services including route guidance, navigation and safety bulletins, improving navigational aid and emergency rescue in their adjacent waters.

Zhuang Guotu, former head of the Center of Southeast Asian Studies at Xiamen University, noted that the provocative move by Vietnam is in line with U.S. President-elect Donald Trump's recent tough attitude toward China.

Zhuang said Vietnam's double standards are obvious, as the country previously issued a set of stamps showing images of disputed islands to reaffirm its own sovereignty. In July, Vietnam also refused to stamp new Chinese passports featuring the nine-dash line, a typical symbol of Chinese sovereignty, according to the BBC. In 2013, Vietnam lodged a protest against the "Beautiful China" stamp series, claiming that one of the scenic images on the stamps was actually in Vietnamese territory.

Zhuang said Vietnam's reactions will hinder Sino-Vietnamese relations. Vietnam recognized China's claim of the nine-dash line and South China Sea Islands before 1974.