Strange "demigod" glitch

[critanium 5]

Date/Time: Tuesday, June 26 7:10pm

What happened: Player invisible in 3rd person, makes no noise or sight, no sense of hunger or thirst, seeing player diamonds 10000m out, silently radioing random numbers... Zombies don't spawn if your the only one in a town or city

Where you were: Novy Lug, heading towards Kratsnotav.

What you were doing: Hiking, entering the server.

*Current installed version: 1.7.1.5

*Server(s) you were on: Didn't record the server, but it's happened on two seperate ones.

*Your system specs: intel core i5, nvidia geforce 560ti

*Timeline of events before/after error: Spawn, realize glitch, hike towards kratsnotav, realize that no zombs spawn, leave.