[962porsche]

there could be quight a few reasons for this to happen .
1st like David stated you just did not prep it right .
some times if the finish is not cured the masking will pull off the finish . but in most cases it should not do that even if the finish is not cured yet . most of the time you will just see an imprint from the masking .
you just may not have sanded it right ? you need to sand every little spot ,nook, cranny,and so on . if you don't sand it the finish will not stick .
even if you did sand every little spot you may have not used the proper grit . some people will sand with a to fine grit of sand paper thinking the finer the better or being lazy sanding with a to course of a grit . if the grit is to fine there is nothing for the top coats to bite into or if the grit is to course the top coat will just lay over the top and not set into the sanding cut . leaving very very small air pockets in the sand scratches were the finish can not bite into .
all under coats that would be primers and sealers have a window from the time you sand them to the time you can top coat with out resanding it . most of the time it's only 24 hours at most . some paint CO's only will give you a 12 hour window before you have to get top coats on there under coats .
what happends if you don't get top coats on is the sand scratchs you sanded in the under coats start to close back up .
it could also be that from the time you sprayed your under coats (primer) to the time you sprayed your top coats you did not wait long enough for the under coats to cure .
what happends then is that there are solvents left in the primer (under coat) that need to evaporate . by spraying on a top coat to soon you trap them under the top coat . the solvents need to get out some way so they start to run them selfs between the under coats and the top coats giving bad adhesion . then it will do two things start to delaminate down the road or if you mask over it the masking will just pull the top coat off the primer .
it could also be there is just a low cost primer that was used . the lower cost primers and sealers have more talc in them and lower grades of binders . by adding more talc it takes the higher solids away . top coats don't like and find it very hard to bite into talc so with out using any sealer over a higher talc low cost primer
the top coat finish will just ever stick .