This occured twice in the same game. The first time it happened I invaded an enemy planet. I won the fight with something less then 50 soldiers left. When I dismissed the ground assault window the planet showed something like 4.19283132 T people. Needless to say my approval was instantly 1% and my influence covered the entire map.
So I went back to a previous save that was just a couple of turns before I had evaded. This time when I took over the planet everything was normal. No overly huge population. Maybe 15 turns later one of the AI empires took over one of the minor race's planets. The same exact thing occured. His population on the planet showed 4.19283132 T and his influence covered the map. This time I saved that file on that exact turn under a different name. However when I loaded that game to be sure it showed the bug (I was planning on emailing it to tech support) it showed everything as normal.
At the time this occured the galaxy was both in a xenophobic period with reduced influence and an economic boom. I tried to recreate it to be able to give you more of an idea of what was going on but when I invaded after the load everthing was fine. And when I loaded the one I tagged as BUG everything was normal. I'm wondering if it could be some sort of fractional error when computing the left over population after the invasion. You know divide by a really small number and get a large one in return sort of thing. But I don't understand why the save file doesn't show this. Unless the save file isn't of the turn I thought. Meaning maybe I should have hit the turn button one more time and then saved.
This is on a gigantic map with 6 AI opponents. It is also a Metaverse game.