What a piece of good news. The mysterious fulvetta has been resolved by the authorities. Thank you to wgeoff to provide this updated input enclosed with the thread which I read with great interest. My first encounter to this fulvetta was on January 29th at Tai Po Kau and fail to name it. After consulted with an experienced watcher and had made references to page 578 of A photographic guide to the birds in Hong Kong September 2010 edition and page 206 of The birds of Hong Kong and South China, we identified the timaliids as grey-cheeked fulvetta.
Apparently more input would be required to supplement the Huet's fulvetta or even the David's fulvetta.
Thank you again to wgeoff for the updated input.