textures don't get updated after editing in external program

Two systems where the update of the file modifications didn't work.

I manage to get a situation where modifying a material texture in paint caused eventually it not getting updated and the file got locked.

Add material to cube and add png image as an diffuse map. Open it in Windows Paint and resize the file to double of the original. Save and observe it changed. Run the Viewer and keep resizing the texture and restarting the viewer. The studio will throw an assert about wrong size texture on exit if you are successful at reproduction.