As the CDN-T2 has two anti-phase transformers in the HF path, this will cause line A to be disturbed in the opposite polarity to line B, referenced to ground. That is for a given pulse, A will be driven positive while B will be driven negative (a balanced signal) with respect to the ground.
By contrast, the CDN-AF2 omits the anti-phase transformers, so the disturbances will be driven in the same polarity with respect to ground, that is, in common mode.
If they are connecting your ground wire to ground, and the other to A (or B), then not a lot of difference will occur between the T2 and the AF2 i wouldn't think.
If they are connecting to A & B without ground, you will see differential voltages due to external capacitive coupling to ground and the series inductance of the cables. Is your circuit externally earthed?