One of the early posts in this thread suggested that the plane could have been tankering fuel and carrying way over the amount needed for "Beijing plus reserve".
Many thousands of posts ago, someone published the price per litre at PEK vs the price at KUL. This along with the assumption that Malaysian receives a 'significant' discount as a state owned* flag carrier suggested tankering fuel on this route was the norm.
(*Malaysian government has a 52% stake in the company)