Within Admin, if I click on Post Tags it shows a list of tags.
If a tag is in 2 posts only 1 post is shown when I click on that tag.
If a tag is in 1 post then clicking on that tag shows 'No posts found'
This behaviour also occurs in my tag cloud on the actual website. Posts with single tags therefore don't show up and a search box with apology is displayed instead.
I've stripped functions.php to a bare minimum, deactivated all plugins, switched to the default theme.
Can anyone else replicate this?