Copy on image into excisting image

[Arne]

When im coping one image into excisting image and edit part of the copied image, there is a change of colour in the background where the removed part of the image used to be.

I have one picture,
adding a layer
adding image of stars into new layer
removing most of the stars/new image
outline of new image is still there

please see attached image

[Ofnuts]

Can you show us the "Layers" list in a screenshot? What is the layer blend mode of each layer (Big selector at top of list, shows th eblend mode of the active layer)? Are they all set to "Normal"?