horace r allen is how he is registered on ancestry ,aged 8mnths there is also a cyril aged 2 on that census.I was told by Dorothy years ago,that he was named after Henry Redvers Buller a captain in the army who was awarded the victoria cross in the Africa Campaigne in 1879.The only explanation i can come up with ,is that he adopted the Buller himself in later years,but he certainly is not registered as Buller as you say,hope this clears it up for you,its a puzzle.