BleepingComputer.com: Instant Messaging Issue (seems To Be Cross Platform/client)

I am using AIM on my home computer for an instant messaging client, and pidgin at work on a Solaris box. Recently, I received an IM from a buddy who asked me why she cannot see my screen name as available in her iChat program on her mac. I confirmed I was not in an invisible state.

A few days later, the same thing happened, except this time it was reversed, I could not see a friend who had IMmed me from work (this is a different friend mind you, and on a Solaris machine. So the next day, I went in to work, keeping my home computer logged in to AOL Instant Messenger. Sure enough, his pidgin client could not see my screen name. I then proceeded to walk over to my computer and log in to my screen name through the pidgin client, and it told me that my screen name was online twice. Does anyone know whats going on here?