Really weird.
There is still something we can check - even it shouldn't be changed by itself - Please, select the image1 material in the Outline window; hit the right mouse button (RMB) over it and select "Edit material..." in the popup menu. Now, tell us what is the value selected for the field "Vertex Colors"?
There is still something we can check - even it shouldn't be changed by itself - Please, select the image1 material in the Outline window; hit the right mouse button (RMB) over it and select "Edit material..." in the popup menu. Now, tell us what is the value selected for the field "Vertex Colors"?