Paint cracking reason?

[ToMeToYou]

So i've bought a car and noticed one of the plastic wing mirrors had a poor paint job on it, cracking sort of look. I've sanded it down and cleaned it up and gone to halfords and bought a new paint can and shook it pretty well.

The cracks are reappearing, any idea why?

[ToMeToYou]

Sorted it by using body filler on the cracked areas.

[fttm]

Plastic , no flexing agent in the paint ?

[Matt_E_Mulsion]

Probably a reaction between the different paints. You might need to 'seal' it with a primer first or sand it back to the bare plastic.