Technology search does not always show the tech required for certain unlocks

v0.77 turn 24, I don't have Constructors yet and don't know how to get them.  I did a search in the tech tree but "Constructors" returns no results.  After paging through the techs I was able to determine that the tech "Starbases" is required to build Constructors.

Just tried a couple others, searching for "Survey Ship" returns the tech "Survey Ships", but searching "Freighter" does not return the tech "Trade Networks".