I set MaxDebris=1 too. On a VehicleType. I as both min and max is 1 it should always apear but it doesn't. Sometimes debris appears, sometimes don't. There is DebrisMiximums=1 set too, i heard it doesn't work but still set it. DebrisTypes= are just one thing.
MinDebris and MaxDebris have some quirks. MinDebris can't be less than 0, MaxDebris can't be less than MinDebris. When getting a random debris count, the game gets a value from MinDebris to (MaxDebris - 1). The function is smart enough to reverse the bounds if max is smaller than min, so for MinDebris=1 MaxDebris=1 this will either randomize as 0 or 1, so 50% of the time you'll get no debris. To create a non-random amount of debris, try DebrisMin=x DebrisMax=x+1.
I'll see to making this more intuitive for the next release.
More details, please. Where did you set it? In what situation should they appear but don't? What are the values of related tags?