You are missing a few
or keywords in the search query if you are looking for posts with any of those tags. Your link leads to a search with the following search string:
[boost] or [boost-phoenix] [boost-spirit] [boost-spirit-qi] [boost-spirit-phoenix] [boost-asio]
This search will find posts that have the boost tag, or all of the other tags you list in the rest of the search string.
To search for posts that contain any of the tags, use a search string with an
or between each pair of tag names:
[boost] or [boost-phoenix] or [boost-spirit] or [boost-spirit-qi] or [boost-spirit-phoenix] or [boost-asio]
The result of this search includes the "missing" post highlighted in the question.