TDR stock from Taiwan

Taiwan friend ask if he can sell his taiwan stock in Hong Kong, which is duel listing in Taiwan and Hong Kong. After consulting the Settlements and Clearance department, the result is negative. There are only on way conversion of the stock, which mean the TDR stock purchase in Hong Kong can be convert into original Taiwan stock, but not vice versa. For example, stock 322.hk is a TDR stock listing in Hong Kong, it could be convert into 910322 in Taiwan, but 910322 cannot be converted into 322.hk. What a pity!

322.HK ----> 910322.TW

910322.TW --X--> 322.HK