Episode #2.2 - S2-E2
Other mistake: Sister Marguerite throughout the whole episode is wearing not very nun-like quantities of lipstick and mascara - especially considering that the head nun is depicted as strict and frowning upon things like chewing-gum.
Answer: There's probably no particular reason. Sets and props on long-running TV shows often change as needed and for various reasons throughout a series run.
raywest ★