I have a simlilar problem, but it happens with MSN and ICQ.
After some time I get disconnected, so the msn protocol icon becomes gray. The icq one shows like if I was away.
If I try to reconnect to msn, it doesn't work. With Icq, the icon changes to the online one, but from what I learned from friends, I wasn't still online.
The only things I can do is close Kopete and re-open it.
It happens randomly.