Steps to reproduce the issue

1. Create a custom field of type editor. Make sure the "Buttons" option is set to yes. Set the editor to subform only.
2. Create a custom field of type subform. Add the editor field to it. Make sure multiple is set to yes.
3. Edit an article where the field is available.
4. Add 2-3 rows of the subform.
5. On the last subform row, use an editor button ("CMS content" in TinyMCE) to insert something like a menu item.

Expected result

Content is inserted in the editor field where the button was pressed.

Actual result

Content is inserted in the editor field in the first row only.

System information (as much as possible)

J 4.2.6
PHP 8.1

Additional comments