CCR and Ghost Cable

Hello, i just installed a brand new CCR1012 wiht version 6.15. After 3 hours it stopped respondin on WAN interface so i rebooted the unit and decided to upgrade to version 6.22 and new firmware version 3.19.
Righ now i only have 2 cables connected ether1 (WAN) and all other ports are bridged with just a cable on ether6 (LAN).
After 1 hour i see in the log that ether4 is up and connected at 1Gb/s, but no cable is connected to it!!!
Any idea??