me not. he said to have implemented the new inset lookup with an optional hashmap. look at the PR commit. it uses a C++ ordered set and map to do the lookups, ie a red-black tree, not a hashmap. either the implementation is fucked up, or the API.
I admire your tenacity -- after a certain hour on a Friday, I try to avoid other peoples diffs :)
the map member used for the lookups is a tsl::hopscotch_map (https://github.com/Tessil/hopscotch-map), which is a proper hash map. so it seems to be the latter, that the API is wrong, but from what I can tell it is only a wrongly named class. i don't see where the API makes guarantees about iteration order, which is where the implementation difference would be noticeable (beyond performance for lookup).