While our heroes repeatedly state that no natural phenomenon can move at warp speed, every show features at least one episode where a natural phenomenon does that very thing. Quite without the help of engines in nacelles...
Again, sounds like you are mightily worried about the ships' lights going out when they reach the ends of their extension cords, or Kirk's toupe falling off if Sulu flies upside down. There doesn't seem to be any point in applying random rules like that on how Star Trek works. The show has plenty enough random rules of its own!
Is there really any proof of this, or is it just annoying fan speculation?