Canvas on an overlay camera doesn't render when base camera target is a render texture.

Has anyone else seen this? The canvas is set to "Screen Space - Camera" and renders as expected when the base camera renders to the display. But if you set the base camera to render to a render texture, any canvas on an overlay camera is not rendered. I put an example project up if anyone wants to see what is going on.

https://github.com/johnburkert/RenderTextureTest