The issue has to do with call "slots" not being freed. So new call activity is accounted for on line 3, line 4, line 5, and so on. As you do not have that many lines on display, you do not see the information.
This slot not being freed might happen if you get a queue call and transfer it out, I do not recall the exact details, but was some specific interaction with calls that resulted in out of order AMI Events. I did some modifications on the latest FOP2 version related to this, not sure what version you are on, I suggest upgrade to the latest and see if you still have this issue.
If you do, then the proper way for us to work on a fix would be to determine when a call slot is not freed, what actions on the PBX lead to that state, so we can track the AMI event log and see if we can fix a bug if there is any, or try some kind of workaround if AMI events are out of order or incorrect.
http://members.asternic.biz/knowledge_base/how-to-debug-fop2
It is important to single out the specific actions that lead to the issue, otherwise analysing logs is kind of impossible as we won't be able to single out the events that cause the issue.
