When selecting multiple tags, separated by "or", the related tags list shows additional tags with their count. Selecting any of those tags does not limit the search, unless one adds "is:q" to the search box. However, adding "is:q" to the search box eliminates the related tags list; thus preventing further refinement.
For example a search for legislation or regulation,
https://politics.stackexchange.com/questions/tagged/legislation+or+regulation
shows 141 questions, with related questions showing united-states with 72.
Selecting united-states shows 112.
Placing "is:q" in the search box shows 72, but the related tags list no longer shows. This prevents the showing of counts or refinement by selecting additional tags. In effect, those tags must be added manually without necessarily knowing what tags are related.
This extends the previous bug report: tag search summary with “or” operators are not parenthesized correctly, to include the loss of the related tags list.
is:q(or any other operator/keyword) causes related tags to disappear even when searching for one tag. It looks like the "Related tags" feature is only supported on/questions/taggedand not/search, which kind of makes sense.