Certain friends on my friend's list have their online status totally blank?

[burnout360]

There are certain friends on my friends list that have their online status totally blank, i mean it doesn't even show if they are online or offline even on their calling card, the area on the calling card where it says online/offline does not have any of that. I know they are not the type to turn off their status and also i have never heard of something like this to occur. i think it might be a bug in the system, if so can it be corrected. They are also missing from my dashboard, i know one is not the type to just go invisible on me though. I am considering it could be a bug in the system.

[luna Datura]

Its because they checked invisable.(show off line) either in friends list  or in pref.(fyi singlearity shows this)

[Alwin Alcott]

if they are also missing on your dashboard they indeed hide their status for you, but if they show up on the dahsboard but keep offline it's a bug, thats around for quite some time