What does a negative Annual Growth Rate mean?

[Jumpp (OP)]

What does a negative annual growth rate on the Population and Production pane's "Summary" tab mean?  I imagined it might mean that, due to overcrowding, the population is declining rather than growing, but I've got such a colony and the population keeps ticking up.  This despite a growth rate of -2.20%, and I'm reasonably certain that no civilian shipping is delivering colonists.

So my assumption was wrong.  What DOES this thing mean?

[Nathan_]

Every planet naturally builds some infrastructure, so that does over time raise the maximum pop limit, likewise civs will deliver both infra and colonists keeping pop up.

[alex_brunius]

and I'm reasonably certain that no civilian shipping is delivering colonists.

Are you sure? If you run longer time increments like 5 or 30 days and the colony is nearby civilian ships may very well have time to make the trip there, unload and then return without you seeing anything.

[Jumpp (OP)]

Are you sure? If you run longer time increments like 5 or 30 days and the colony is nearby civilian ships may very well have time to make the trip there, unload and then return without you seeing anything.

I'm reasonably sure.  Here's what I know:

- The colony has a posted Annual Growth Rate of around -2%, and has for years
- The colony's population has grown from around 69 million to around 73 million in that time
- On the Civilians/Ind Status pane, the colony is marked as a Source of colonists
- The amount of infrastructure has been slowly growing, though never by enough to get the "Population Supported by Infrastructure" within a few million of the current population.
- The logs of civilian shipping lines show several pickups of colonists from this colony
- The logs of civilian shipping lines show no deliveries of colonists to this colony

I'm starting to suspect a bug.  I can't figure out why the population of this infernal colony keeps growing.