I have experienced this minor problem for a while and it has been discussed on the Tesla forums here and here. I assumed that with the 4.5 software this problem would be fixed once and for all. But alas with 4.5 the problem is still there.
The issue is if you have your backup camera in the top half of your screen and then decide to open up your garage door, the homelink button turns the camera to grey and you can’t see anything.
A few times the window has shifted, but at least for me most of the time, the camera goes grey instead. I have no idea what causes the window to shift and why it does not occur in all cases.
The workaround is to always have the camera in the bottom half of the screen. But with different screens, things often get juggled around.