Being "online" is based on recent activity (i.e. refreshing pages) rather than being logged in or out. So if you've done something on Neopets within a certain period (probably the last 15/30 mins) it'll show you as online and if you haven't done anything within that period it would show you as offline.
Weird... I will try again today, see if it happens again, anyway thanks for the support.
Just changing a little the subject, there is something that i could do to reduce my enormous ping delay without tunnel softwares?