[Bug/Savegames] Reloading save removes empire tree

Had this happen several times - from a game, if I go back to the main menu and load a save game, when the file loads empire tree simply disappears.

I've had it 'partially' reappear, with a unit I selected to move showing up, or a city that hit the end of its production queue, but quests vanished entirely, and the display looked odd for the partial reappearances (no category headers).