The text between the parentheses of section:() isn’t the name of the section you want to search in. It’s the search terms you want to match only if they’re in the same section.
So section:(animals plants) finds occurrences of “animals” and “plants” that appear together in the same section. It would match the first and second sections in the following example, but not the third:
## Likes
- Animals and plants.
## Undecided
Not sure how I feel about squishy animals.
Big plants intimidate me, but I don't know if I dislike them.
## Dislikes
- Loud animals.
So section:(ideas) is the same as just searching ideas.
I think section:(ideas "- ") should do what you want, but when I try it I still get unwanted results. They are different results from your search — the correct ones appear at the top, but then there is more after them.