query_vars is not necessarely representative of the final query_vars used to build the SQL query

[msaggiorato]

I've recently stumbled upon a case here where the post_type query_var changes over the process of the query building process, and the change is not reflected in the query_vars variable of the query.

On the section highlighted ​here (sorry for pasting a GitHub link, i just wanted to use the section highlighting feature), you can see that if there's no post_type set in the query, but you're querying taxonomies (eg a tax archive query), the post_type is set (using a separate variable), and then used on the ​following section to build up the where statement.

In my opinion all of the query_vars modified during the process should be reflected in the query_vars variable, so you can after see the actual value being used for querying (on the posts_request filter for example).

You can see ​here a section where the $q['author']}}, {{{$q['author__in'] and $q['author__not_in']. These is an example of changes that are not reflected in the query_vars (since there's no call to fill_query_vars after all this extra parsing, sanitizing, and defaulting process is made).

Let me know your thoughts.