Yeah, but it's an error that's become a canonical truth for the Anglophone cartoon (much like says blue eyes on 'Bots and red eyes on 'Cons, Jetfire being called Skyfire etc.). Also Rumble was distinctly purple in the cartoon, not blue like the Frenzy toy. And MP Frenzy is very much purple, modelled after G1 Rumble's (or Frenzy in JP G1) colours... so it would be perfect sense for Hasbro to name the purple robot Rumble since the toy is coloured just as Rumble appeared in the Anglophone cartoon. It would also help differentiate the toy from the TakTOM version. TakTOM's already going for RIRFIP (which makes sense for their market), why not go for FIRRIP on the Hasbro version?
Yeah, that was frustrating... now they seem to have settled on basing them on their United toys, which is RIRFIB... so I've accepted it as so. The flip flopping has been most annoying though, I agree. Gah.