Piston door bug when you power them

When i power some pistons to create a piston door it appear a bug with sticky piston's arm...http://imgur.com/DXng0,x5yvq,QvwbS in first photo pistons aren't powered, in second photo pistons ARE powered but a the dirt block don't show up, in third photo pistons aren't retracted and the dirt block is showing up....Sorry for my bad english.Thanks.