If NeoPixels are created without specifying a bpp or a pixel_order:

pixels = neopixel.NeoPixel(board.D18, 8)

then this would get used:

 def __init__(self, pin, n, *, bpp=3, brightness=1.0, auto_write=True, pixel_order=None):

so you end up with bpp=3 and GRBW for pixel_order, which is bpp=4.

This is my bad, since it was introduced with #24 to fix #1. I think there was some attempt to maintain backwards compatibility with the older style of using bpp only. So that's why both bpp and pixel_order are still there:
#1 (comment)

But might be good to somehow check and protect against this:
https://forums.adafruit.com/viewtopic.php?f=47&t=151980