Set Tracker to Specific Device Index Issues

I'm using the SteamVR Camera Rig with four trackers, and I want each tracker assigned to the correct device index programmatically instead of using the Vive Input Utility.

I'm currently using this function:

Code (CSharp):

1. obj.GetComponent<SteamVR_TrackedObject>().SetDeviceIndex(index);

where index is the device index for the tracker that obj should track.

When I print which tracker obj is tracking every update function, its device index is set to index for 2 frames before it is set to another device index.

I'm wondering why it changes after 2 frames, and if there is a way of making the tracker track a specific device index by setting it only once?