Different Login time in different reports

Hi,
When i am viewing "Agent Performance Detail" report i see complete detail of all agents including login time and all other things, and when i click on the any individual agent to see that agents detail on that page i see different login time.
Is this a vicidial bug or system bug. What could be wrong in this.
Looking forward for a positive reply.
When i am viewing "Agent Performance Detail" report i see complete detail of all agents including login time and all other things, and when i click on the any individual agent to see that agents detail on that page i see different login time.
Is this a vicidial bug or system bug. What could be wrong in this.
Looking forward for a positive reply.