In 2017 WikiEditor, __while CodeMirror is disabled__, the editing while a page is scrolled down is okay. However, I was trying to [[https://en.wikipedia.org/wiki/Drag_and_drop|drag a content]] of a page, like an [[https://en.wikipedia.org/wiki/V|article about letter "V"]].
Scenario A:
# I was dragging just one word from one place to another.
# I right-clicked to open a menu and then selected "Undo"
# The same word appear twice, once in its current position and once in its previous position. (seen in a screenshot)
# I clicked again, and one of them disappears.
# The word still appears in its current position.
# I clicked "Undo" numerous times, but the word won't go back to its original position
{F16114596}
Scenario B:
# I highlighted and then dragged just one word from one place to another over and over.
# I right-clicked to open a menu and then selected "Undo" many times.
# In one occurrence, the same word appear twice, once in its current position and once in its previous position.
# I clicked "Undo" numerous times, but either one clone/copy disappears, or the editing went weird. (more at other screenshots)
{F16114984} {F16114983}
Scenario C:
# I highlighted and dragged the whole paragraph from one place to another.
# I clicked "Undo", and the paragraph goes back to its original position.
# I clicked the editing window again, and the paragraph disappears.
# 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