I have had that happen once, when a gunsmith with little CZ experience forgot to reinstall the retaining pin. It only took one or two magazines full for the hammer pin to move so far out I felt it on my thumb, which is how I knew something was wrong.
Just to clarify, you said it is a relatively new gun, but:
1. Are you the first owner?
2. Have you disassembled it and removed the sear cage at all?
3. Has anyone else disassembled it for any reason at all?
I haven't had mine apart in quite a while, but my recollection is the retaining pin is trapped in its hole when the sear cage is installed, so there is no way for it to come out when assembled. Either it was never there, or it was never re-installed after someone had it apart.