FWIW, my shafts are 1/2" and tapered to 3/8" with hand forged Tudor bodkins.
I think what I'll do to avoid this in future is buy the shafts 1/2" parallel and taper them myself. If the density is low, therefore making the overall weight less, I'll leave the taper later on the shaft, keeping the first 2/3 or so 1/2" more or less, then a steeper taper towards the nock. Cheers for advice though guys.