REBOUND_IMMUNE shot property makes the shot glide along walls.

[Loobinex]

Giving a shot a REBOUND_IMMUNE causes the following behavior:
https://github.com/dkfans/keeperfx/assets/13840686/83d6cf3d-f814-4e4f-a827-faa17f3f0a39

Observe the arrows glide along the wall instead of hitting it.

I suspect this is caused in the thing_fire_shot function, specifically in this piece of script:

    if (((shotst->model_flags & ShMF_StrengthBased) != 0) && 
       ((shotst->model_flags & ShMF_ReboundImmune) != 0) && (target->class_id != TCls_Door))
    {
      flag1 = true;
      pos1.z.val = pos2.z.val;
    }

At the end of the function, this follows:

      set_flag_byte(&shotng->movement_flags,TMvF_Unknown10,flag1);