Images that can't be altered: ghost images in the software

There’s an “image” in my blend file that Blender won’t allow me to paint on. Look at the screen:

In reality I think this is some internal database problem and somehow the entry for “test2.001” never got discarded/updated/whatever. But why does Blender present the Image name in the Image Viewer in Paint mode if it’s not going to let me paint on it?

EDIT: or do I have to save a blender generated “image” to disk before I can paint on it??

Such problems are difficult to figure out just by looking to a screenshot… A file would be better.

In your Image Editor sidebar, what does the ‘Image’ panel shows?
If source is a ‘Single Image’, then it has to have a link to a file. If you’re creating a new image, the source should be set to ‘Generated’ (and you don’t need to save the file prior to paint it, but you should save it before exiting blender).