It can easily be fixed though. The 'problem' is that basically the contact area of the firing pin is too small for the Prvi primers. The Prvi primers are softer/more sensitive than the French military primers. The MAS 49/56 has a floating firing pin and as the bolt goes forward the pin contacts the primer (pretty common with a lot of milsups). The fix is to basically flatten the tip of the firing pin slightly. Look on some of the milsurp forums and you'll find more detail. It isn't hard at all. Also replacement firing pins are cheap and readily available.
Christiangunner, if you ever make it to the OKC area, Kings Pawn in Del City carries Prvi MAS 7.5x54mm ammo at pretty good prices. If you reload the Prvi brass is good too.