hi..
I unplug my eth0 lan cable.. and suddenly my system shutdown... no idea 
Was it a kernel panic or just a normal shutdown?
no, its normal shutdown.. quite strange.. I tried to /etc/init.d/network restart
it also shut down the server.. look at the messages log.. I couldnt find anything strange... 
Do you have some sort of cluster service on this machine that tries to fence/disable the node?