I was given a bit of grief at the airport a couple of weeks ago. I am picking up my daughter over xmas and bringing her to see me (separated; you know how it is). Doing the outbound turn around and come back with the kid. Do the same in reverse at the end of the holidays. Booked return on same itin with kid, so I end up with two back-to-backs. Now, the route no longer has a saturday night stay requirement (thanks LCCs), so I don't know what the issue was. The agent, who issued the tickets, said that I was OK though because I was using those free round trip VDB vouchers, so there was no higher fare that I was avoiding. Clearly, saturday night stay rules do not apply to VDB free trip vouchers. Something to consider when planning your future trips.