Strange Flying Broadhead

[2B4Him]

This is my first year using fixed broadheads and I noticed something yesterday while practicing.
Background info: From someone's advice here on the GS, I have numbered all of my arrows. All of my arrows are identical - same brand, size, etc. When using field tips, my groupings are all good, no irregularities. But yesterday, in three separate groupings of five arrows using practice broadheads, my #6 arrow kept hitting about 2" away from the others (once to the left, twice below). The arrow doesn't have any noticeable problems (the vanes are fine, etc.).
Any thoughts?
I have retired #6 from broadhead shooting, but is this something that is unusual?

[Destry]

spin test it and check for a wobble, you can also try switching it to another shaft and seeing if you are getting the same results

[Mojo]

That's why they are numbered, pick the ones that fly best with a broadhead (when huntin')
if it shoots good with a fp, leave it for practice....
if it shoots good with a bh, fling it at game...

[JW]

Good move shootin em all first! Like above spin test. Tinker a little. If it dont work down were you numbered it on the fletch write the word "coon" !!