the object tracking seems not stable

[lzzhangar]

First great demo app thanks. I noticed that the object tracking isn't stable. Here are a couple of observations:

1. After bounding box was chosen, the bounding box of the tracked object kept shrinking (getting smaller and smaller) even I didn't move the camera.
2. If I moved the camera to make object off the screen and back to be on screen again, the bounding box disappeared.

Are the above known issues of vision framework or issues with the coordinators?