If I want to clone from one image to another I use copy and paste. First I open both images as separate images. Then using free select I outline the area I want to clone and then copy (Ctrl C). Then I go to the other image and paste (Ctrl V). It appears as a new pasted layer that I can move into position. The pasted layer can be scaled, color adjusted or other before merging the layers.
edit: missed that in the previous post!
edit: missed that in the previous post!