My Stellarvue 70ED suffers from this, and I have also only noticed it while shooting the HH and/or M42.
I believe this is a reflection from the internal [edge] of a lens element, which are never very smooth and often have tiny chips and grind marks, hence the striations in the reflection.
I'm not sure what the top APO manufacturers do to reduce this, maybe they etch and then blacken the edges somehow to scatter and absorb the light.
The scatter would obviously affect contrast but it's much preferable to the rainbow
Maybe they sacrifice some aperture by stopping the lens down enough that the edge reflections never make it thru?
Not a great drawing, borrowed from a quick google image search, but I think it conveys the idea: