Commands like those of the the insert/delete widget, bubble up to parent containers.
Most likely you do not have a containing section around your optional section, so the commands are bubbling up to the section you have around your entire form. If you right-click on some blank space within your form, you will see commands like "Insert X". The X will help identify the offending items (you already know that you at least have your optional section as an offending item).
Typically (but not always), if you just move your optional/repeating item inside another different container this will go a way.
So for example, let's assume you have the following data source:
Root
- Items
- - Item
- OptionalItem
- SomethingElse
Let's also assume that you have a section bound to Root which contains all the rest of your form inside of it.
If you place a repeating table for Item inside the Root section, the repeating table commands, such as "Insert Item" will appear on the Root section as well--these commands bubble up. To prevent this, insert a section for Items, and then place your repeating Item table inside the Items section. This will stop the bubble up at the Items section and it won't keep bubbling up to the Root section.
If you place an optional section for OptionalItem inside the Root section, the command to Insert OptionalItem will bubble up to the Root section. To prevent this, since there is no parent node, except Root, above OptionalItem, you can create a containing section from a sibling node. So Insert a section bound to SomethingElse, and then place your optional section inside that. This will have the commands bubble up to the SomethingElse containing section, and stop there, preventing them from reaching the Root section.