Reporting discrepancies?

I am trying to figure out how many opens we had for a recent campaign, and I am getting different results depending on where I look for the information.

The email program dashboard and email performance report give me one number, but when I generate different reports to see WHO opened the email the total numbers are different. I am actually seeing three sets of numbers: one number from the dashboard/email performance report, one from the campaign results from the control panel within the campaign, and another from a group smart list.

Anyone else ever see this?