i don’t think there’s a bug here.
i don’t think iNat’s search is designed to search specifically for names in a G. species pattern. instead, it seems to usually be searching for names which include words that begin with the letter combinations you input.
in your case, “arborea” begins with “a”. so the “a” is sort of redundant, and an “a arborea” search effectively is going to just return any taxon with “arborea” in the name.
but you can search for “ame arb”, and that should be more likely to return Amelanchier arborea as one of the first results:
