Yup.. - you are correct, Rainman..
I was suspecting it to be "the invisible mode"
And then .. - ya.. - it's not working - cuz i clicked on the person profile .. and was able to see him there too.. and for him instead of "On line" there, it said "Invisible" instead....
Some people, i guess, simply prefer to hide....
What for? (i actually know / suspect why... - but that's another old story.. and will just let it remain like that)...
Let it be.. .. and basically, wanna be invisible - be it!
(as soon as this feature is fixed i guess)