That's not a big prob.
Usualy when I use the command "switchLight", the lamposts begin to have an irregular behaviour, everytime I retry the mission (either in editor or single player mission). The same aplies when I destroy a lamp post - surely a bug from OFP.
If you really want those lights to be shining, use the command "switchLight":
_LampPost switchLight "ON"
or
object _ID switchLight "ON"