Should The Devil of Christmas be with the specials and not series 3?

I know it was aired a couple of months before The Bill, but the BBC website has it listed as the first episode of the third series, as does the IMDb and Wikipedia. Also, TVDB has it listed with the third series, not as a special episode with Dead Line.

As each series contains six episodes, both on TV and on the DVD/Blu-ray releases, I think this episode seems out of place in the Specials and would be better with Series 3.