Reproducer attached.

Steps to reproduce the issue : 

1. Run the example application.
2. Drag "layer_1" and try to drop it between "layer_2" and "layer_3".
– There are two dropping points between layer_2 and _3, OK to drop it to either point.
– The operation will be ignored, and "layer_1" will be put back to the initial position.

3. Expand "layer_2", and scroll the view by quickly dragging the slider of the scroll bar.
You will find an item wrongly indented somewhere in the layer_2.
If you don't, repeat the steps 1-3 until it happens.

4. Once you fell in this situation, you will see the wrong-indentations here and there while you moving the slider of the scroll bar.

The attached screenshot shows how the issue looks like.
Although Feature_2_41 was displayed in a wrong indentation, the data model was not corrupted as you can see in model_structure.txt.