It looks like the ntpd doesn't get the correct time with WiFi. My Raspberry Pi's are connected via WiFi dongles (which work without problems) to my network.
The odd thing is, I read that the time should be on "Jan 1, 1970" if it doesn't work correctly. But my time is always on "Jun 13, 2013"...
When I perform the command:
sudo dpkg-reconfigure ntp
or wait for a while it gets the right time.
Maybe the ntpd starts before the WiFi has connected successfully? Can I change this in an easy way?
I found something similar, but it was for Arch Linux which doesn't help me.