This is what in painting we call fish eyes
It may be that there is oil or some sorth of chemical that is reacting from the paint to the surface
And is more likely that you are spraying it on to thick being a small surfac you concertrate on the smaller area and dont spreed it out quik enough causing a build up ,
So strip it back to bare , then wipe it down with either metho or white spirits , let it dry totaly and then spray paint a dust coat(should always dust coat every thing you spray first time around) Dust coat is a quick spray held further away than you normally would thu causing the paint particals to dry b4 landing , leaveing a dusty look on the surface let this dry repeat once more then give a few even sweeping coats dont foucus the spray on one point it will cause build up and seperate,
(I am a painting teacher so forgive my rant)