First taxonomy term missing

Since I upgraded to 5.x-1.6, the first taxonomy term in a filter or exposed filter is missing, it displays all other terms, but the first term for a vocabulary (any vocabulary) is missing from the select list.

Is this a known error? or am I doing something stupid? (I can't believe it's me, the view worked fine before the upgrade).

If I attempt to make a new view with a taxonomy term as the filter (or exposed filter), the same thing happens, the first term in the list does not show up.