While I was trying to see if I could salvage my save games from the Disappearing Map on Load Bug, I first loaded my most recent save game, then I loaded a much earlier one to see if that one was viable.

Upon loading the earlier game, I was researching the tech I was researching from the later game, even though that should not have been available based on my early game's present tech tree (light Weaponry, in this case). 

I pressed End turn , and the next turn it said I had unlocked two new units ( a few light weapons) but these were not available when designing units.  Also, my tech screen research slot was now empty, and said "slot available".

Note:This was during the disappearing Map detail bug, as the earlier save game was still afflicted by that.