when you wired the light up , which way did you do it
did you run an earth wire to the buld , then a liver wire to the switch , and live from the swith to the bulb

OR did you run a live wire to the bulb , and a earth to and from the switch

either would in effect work , but may cause some problens with switching if you were switching earth off and on

and a second question , is this a double filliment bulb , or do you have any other bulbs in that light fitting ,

are any of the bulbs LED