In 2017 WikiEditor, while CodeMirror is disabled, the editing while a page is scrolled down is okay. However, I was trying to drag a content of a page, like an article about letter "V".

Scenario A:

1. I was dragging just one word from one place to another.
2. I right-clicked to open a menu and then selected "Undo"
3. The same word appear twice, once in its current position and once in its previous position. (seen in a screenshot)
4. I clicked again, and one of them disappears.
5. The word still appears in its current position.
6. I clicked "Undo" numerous times, but the word won't go back to its original position

Scenario B:

1. I highlighted and then dragged just one word from one place to another over and over.
2. I right-clicked to open a menu and then selected "Undo" many times.
3. In one occurrence, the same word appear twice, once in its current position and once in its previous position.
4. I clicked "Undo" numerous times, but either one clone/copy disappears, or the editing went weird. (more at other screenshots)

Scenario C:

1. I highlighted and dragged the whole paragraph from one place to another.
2. I clicked "Undo", and the paragraph goes back to its original position.
3. I clicked the editing window again, and the paragraph disappears.
4. You can't "Undo" the action as there would be no more actions to undo.

The syntax highlighting mode makes editing in 2017 WikiEditor worse, which is explained at T190720