Bear traps (and possibly mines) are not persistent.
It looks to me like normal item rules apply for then, even if they are set up and armed.
This makes it hard to set up ambushes, and almost impossible to secure camps.

I tested this on Exp server UK 0-4. Placed the trap in a position where it was covered by grass, and the chances are ultra-low that anyone would go there, but close to a structure, si i can be sure i got the exact location.
It was still there and armed after around 5min, but gone after around 1:10h.
I left the server in between, so i might have missed a restart.