Query\Grammar::prepareFieldsForQuery() renames a->b to a.b by assigning the new key and unsetting the old one:

$values[$newKey] = $value;
unset($values[$key]);

For a sort specification this appends the renamed key, so orderBy('traits->colour')->orderBy('name') is sent as {"name": 1, "traits.colour": 1} and the requested primary sort silently becomes the last tie-breaker. Fix: rebuild the array preserving the original key position (same for the .id to ._id rename). Add a test with two sort keys.

Filament feature this fixes: sortable columns on embedded-document attributes (TextColumn::make('traits.colour')>sortable()). Filament rewrites the dot path to traits>colour and always appends a secondary default sort, so the user's sort is lost on every such column.