It's a tuning issue. The bow and/or BH's aren't tuned properly. Is there any wobble in the broadhead when you spin the arrow? If there is, there shouldn't be.

If your bow is perfectly tuned, and your BH's are perfectly tuned, they should hit in the same spot... BUT, there is another school of thought here as well...If the BH's are grouping well, do what he's been doing and resight....But you should be able to tune that out..