Opacity Texture: flickering line issue

Hi friend, I'm currently having a small issue when using an image with an opacity texture. 

The setup I am using is the following:

1. An unlit material with opacity texture enabled.
2. An image object with the unlit material assigned to it.
3. An image texture and opacity texture assigned to the material.
4. This image object is then bound to a Head Binding.

This issue I am seeing is a small flickering line at the top of the image object. It appears to be the background of the image texture peaking just over the top of the mask.

I noticed that if the head binding loses tracking of my head, the masked image will freeze and the line will top flicking,but remaining in whatever state (line visible or not visible) it was in when the image stopped tracking.

My guess is it's a bit of an image/mask like rounding error or something. I have tried various things with the image texture and mask (they are exactly the same size), but nothing seems to get rid of it. It's only maybe 1px in height, but driving me a bit crazy as I can't stop seeing it. Additionally, it does not appear on the sides or bottom of the image.

Also, just for reference I am doing this to save file size, using two jpgs vs one large png with transparency.

Any idea what is causing this issue, or how I might rectify it?

Thanks in advance for any help!