I never look at the population growth on my planets. I'll keep an eye on them from now on though...
I don't know what would cause this.

Class 4 has ~2.5B, class 5 about 4.5B etc

I think that this is inncorrect.

As long as the pop is below the cap for a planet, it will grow that turn.

No. A low approval rating on the planet can also stop its growth.

A double thanks and way-to-go Iztok Bitenc, I didn't know there was a Pop. cap, manual does not mention this, nor did I know there was a Wikipedia, very good!

Well this changes everything, I'm going to have to go back and change my strategy some. I was going to use these smaller class planets to fund my needs, I was making over 1000bc a week and was looking to at least triple that, but I see that's not going to work.

Excellent again Iztok Bitenc.

That would explain this statment "This figure may only reflect maximum growth-achievable population." in Wiki that made no sense to me if this statment in Wiki was true "Each planet also has a maximum population based on planet quality.". Not verey clear even after you understand what it should mean, because the only way you would understand this is max pop cap, not growth.

So I'll try that out and see how it works, I just happened to finnish researching Planetary Invasion.

Yes but the idea is somehow stupid. I mean, if a planet food supply supports pop, it should grow. In reality (earth) pop even grows in places where it cant be supplied with food. Sorry to be so blunt.

So that should be changed. Some games even grow the pop beyond food supply (which is normal anyway) so that gives you something else to worry about. More realistic, really.

The strange thing is that while there may not be room on a planet to grow you still can transport pop there and survive.

But then I'm a strange one, I find those kinds of thing make the game more interesting and fun, I don't care so much about reality in games, sometimes I think it sucks the fun out of them. For me their like easter eggs, like in Civ I and Civ II.