Yesterday, my Population Limit was 11090 and my Barracks was busy building troops, so while maxed my population, ~1000 units were queued up in the Barracks.
I destroyed three level 4 nobles, (60 pop each), thereby lowering my population by 180 settlers. So the Population limit of 10910 is correct, (assuming the 11090 was correct to start). I ran a Roaring Bull adventure, losing around 800 troops. I could see the population counts were wacky, but it was late, so I went to bed.
I logged in this morning to find my population maxed at 10910, but 1,537 unemployed settlers. I'm not sure how we arrived at that number, or why it would let me create ~1,350 more settlers than my highest population ever, but ... thank you?
This population issue was introduced a while ago, when PvP was implemented.
We did not want to delete any military units because it could have dramatic effects, so we decided to artificially balance the population.
In most cases, this results in extra population. It will eventually balance itself and your population count will be correct again.