"Plus" symbol appearing on an insert form that links to a new window ?????

I have set up an insert form that includes some select_single drop down lists that are populated from another table.
I am getting a "plus" symbol next to these fields. When you click on the plus symbol it opens a new window that lets you insert a new entry in the table that is generating the drop down list. I don't want this to appear but I can't see what I have set that is causing this to appear.

First image shows the plus symbol on the form
Second image shows what happens when you click on the plus symbol



Just checked the manual

Section 7.2
If the user has insert permissions on the lookup table, a + button is displayed close to the dropdown menu, allowing the user to add a new option to the menu without leaving the current form. If you have, in the same form, more than one lookup field referring to the same table and you have used the + button to add an option to one of them, the other ones are not updated with the new option (they will be when you reload the form, though).

I don't want this feature on my application, is it possible to disable this?