Input field "image" with an additional image as setting with strange behaviour


Building a more complex element with two images based upon input field “image” (call it “main image”), second as a setting with the field type “image” (call it “preview image”, actually it is a video, but that’s not important).
I just discovered: selecting an image for “main image” and save the resource, the second image (“preview image”) contains the same value as the first one. You can see it after a reload of the edit page in the backend.
Then you have to delete the wrong image and save. Now it is okay.

version: CB 1.8.3, MODX 2.6.5
I know it’s not up to date, there is in the moment no maintenance contract, so I have to wait for it.