You're clear over the yellow needs to be the kind that has an activator to create a protective barrier. If your clear is just like your yellow except with no pigment (in other words the kind without an activator), it will wrinkle. The solvents in the new layer will dissolve some of the old paint layer and make it wrinkle. This is basic paint knowledge.

For example if I am painting a frame with yellow paint that is not catalyzed, and I put a catalyzed clear over it, all is fine. If while sanding the protective clear to prepare it for a smooth glossy final clear (or most likely 2 coats of clear) and I sand through the clear and scrape the yellow below, I can't just put more yellow on, I have to put some kind of catalyzed paint on first or when I apply the yellow again it will wrinkle the undercoat yellow, This wrinkling does not happen ever time but it will most likely happen unless an activated paint is an in-between protective layer.