1- Open grid (A)
2- Open another grid (B) and "copy view"

3- "Paste" grid B in grid A

4- Save or close grid A and reopen it just to make sure grid B is still there, that everything is working as expected

5- Focus on the grid B pane (inside A), and close the pane (using "X" button at right of pane) so that grid A is now without any added panes

 5b- Grid A should now be a normal grid, without any panes.

 

6-Save and close grid A

7- Reopen grid A : the grid B pane reappears.

(didn't find any workaround, except replacing grid B with some other grid (like an empty one) or just closing the reappearing pane each time.)