Camera movement causing UI Pointer Enter/Exit triggers to break?

I've got some UI Images that are supposed to change color when you mouse over them, attached to Unity's new UI Canvas (Screen Space - Overlay). It works great until you move the camera, after which the Pointer Enter and Pointer Exit triggers don't fire. After clicking anywhere on the UI canvas, they start working again. I feel like this is some kind of focus issue, but I've got no idea how to fix it. I tried changing the Image objects to Buttons, but the same problem occurs.

Here's a 30-seconds video demonstrating the problem: http://youtu.be/j2nSuyYqwDk

UPDATE: FIXED

I fixed this by disabling "Send Navigation Events" on the EventSystem. What was happening was, the camera was controlled with WASD which was firing off Unity's navigation events (like when you navigate a menu with a controller). These navigation events were inexplicably calling "Pointer Exit" on every object in the scene, causing all my events to break. Since nobody is going to be playing my game with a controller, I'm not worried about disabling the navigation events.