Hello,
I think I already pointed this out on GitHub for a previous version of Grid but was later fixed for allowRowDragAndDrop = TRUE. Now the problem has returned while initially the drag and drop is allowed on grid but then turned off.
To reproduce:
1.) press the button "toggleDragDrop"
You should see that "colSpan" attribute is not correctly updated.
UPDATE: "colSpan" is not the problem. The problem is that Grid Doesn't remove / hide the element with class .e-rowdragheader.
BR. Marko
Edit: I would also like to point out that something tends to go wrong while hiding / showing columns with "ColumnChooser". I did not prepare the example but will do if you are unable to reproduce the scenario.