Negative value for flight mode?

I have a strange question:
I fly gliders equipped with APM 2.5 for several years and I’m very happy about it.
Recently I made a mistake with Mission Planner by defining “Flight mode 4”.
Instead of 12 for Loiter, I taped -12 (négative value).
And surprisingly in this mode the plane was flying very well, like with circle, but with a very strong
bank angle (my value of LIM_ROLL_CD = 6000), but without GPS correction of the center of the circle.
That is exactly what I was looking for: a high bank angle and a short loiter or circle radius, but I would be happy if the glider could correct the drift due to the wind with the GPS.
Therefore, I don’t understand why the software accepts a negative parameter value, and what is exactly happening with this value.
Could somebody help me and explain me what happens withe a negative value of the flight mode number ?


Thank you for all the work you have done.

Gérard Schumacher