The studs were pulling out on my Aria bass when it arrived too. I simply epoxied in every stud but the one the ground wire connected to, as I figured I might need at it at some point in time.
Presumably one of these things that should be pulled off with strict tolerances, but isn't. From memory the studs are tapered, but of course the hole isn't. A tight hole will push the stud out, and slack hole will allow the stud to Jimmy out over time. Threaded inserts would be an ideal solution, but require more skill and patience to install than simply driving a ribbed metal stud into a hole and hoping everything stays put.