Added image appears in an unexpected position in the structure tree

[matthias-ronge]

In the example, an image was scanned in the correction step. In the structure data tree, the new picture (here with the label 1 : -) is inserted after the first and before the second sub-structure element. At least that's surprising. In the gallery on the right, the image appears (correctly) at the bottom, in “unstructured media”.

Goal: The added image should appear at the bottom of the structure data tree, under the last sub-structure element.