Baader bcf filter for 450d ?

[Hungovergraham]

Hi all,I've given my 450 to a Camara repair shop local to me.my question is now given Camara over with bcf filter to replace ir one I've had a call yesterday saying they can't get focus as bcf is thicker than ir one that's in there so they need Shims into it to put it back in true focus I didn't think you had to do any thing else but remove and replace has any one else had a prob with the bcf filter on a canon 450