DOF for first-level analysis

Dear Conn experts,
I work with single-subject analysis and I have a question about resultsROI_Subject00*_Condition00* matrix. This matrix contains a field "DOF" (degrees of freedom). The problem is that for different conditions this field has the same value and I can't understand why, because my conditions have different number of scans.
Could you explain, how this field is computed? Because I have no idea how this is possible.

Thanks in advance for your answers.