Just a little bump... it's not a myth. It's very much true. There's a favourite picture of Rota wheels, some Subzeros, that were used only on track, and really hard on track, for 2 years, and had no issues.
The owner, who we know, had them powder coated to sell on. First time out for the new owner they twisted.
Yes, it is possible to powdercoat a wheel safely, but not all places are aware of the heat treating a wheel gets in manufacture giving it a large portion of it's strength, and re-heating to a fair high temp for a prolonged period effects the structural properties.