npm install installs everything in package.json but we have different dependencies based on what database you pick during node app --setup (redis, mongo, level). Usually just running npm install is enough but in this case there were changes to the database dependencies.
In v.0.7.1 & v.0.7.2 correctly count posts in old structure of sub category.
But if create new category & create post in sub category - counter didn't "see" posts in subcategory & didn't preview posts in main page.
Bug report in git - https://github.com/NodeBB/NodeBB/issues/3368