Mystery texture

I am working on a project, where we are annotating 3d models of scanned real-life objects, with the aim of creating a 2d catalogue. To wit, a layout tab has been created in our template files. These template files are copies of template files from previous projects, edited to suit our current projects needs.

The mystery (question I’d love to have answered) is this: As I was editing the template files’ layout tab, I noticed what I at first glance thought was a glitch. Switching between Shaded and Rendered views of the layout tab (I have the SetDisplayMode command set to custom keybinds), revealed a, for lack of a better understanding on my part, “ghost texture” in the lower right corner (see screenshots):

Above: Rendered view (no ghost texture).

Above: Shaded view (ghost texture).

The reason I call it a ghost texture is because it doesn’t appear to be a plane or any kind of object with a custom texture material draped over it. I simply cannot select it. I’ve tried “ctrl+a” with all layers unlocked and visible, followed by the “hide” command and thus hidden every object in the template file - but the little image remains.
So, I thought it might be a custom background, attached to the “Shaded”-viewport properties. Looked in the settings, but couldn’t find a direct reference - nor are there any files matching what I see in the Layout tab present in the template file’s “_embedded files” folder.

I’m really at a loss here. Can anyone explain this? Is it possible it might be an old texture, permanently baked into the template file?

EDIT: I tried deleting the entirety of the contents in C:\Users\Username\AppData\Roaming\McNeel\Rhinoceros. It reset a lot* of my custom settings but it didn’t remove the ghost image.

*: As in, “a lot” a lot. I could cry :frowning:

Hello can you please post the file or send to with a link back to this topic in your comments?