Heres how I killed everyone:
A Class 10 planet had 24 million people on it, they were overpacked and understantably unhappy about it. What fed all these people was a single Tile of +300% food, with a xeno farm on it, and the colony tile (giving me 29 MT of grain/week and even more room to grow, not bad for one tile).
So.. being the responsible ruler I dissasembled the Xeno Farm, planning on juggling my food stocks to maintain the level I've got and not grow anymore. That left 5 MT of food (from the colony tile), and an end of turn. I knew it would be ugly when I hit next turn....
POOF! population: 5 Million. not a tear in the house... not repurcussions, no shame shame, no population chart plummet. just 19 million people dead, business as usual....
.... can we say bug? well, maybe not bug, but something a beta tester should have tried so it could have been identified and fixed in the code or whatever... I mean I should have at least got a guilt trip GNN report or something!! And the fact a good 10% of my population vanished over a 1 week period should have shown as a verticle plunge in the population history-chart.