Hive re-Queened itself...

I installed a 3 lb. package on 4/11/09 into a brand new hive with undrawn foundation) and upon inspection today, I have swarm cells present... (One of them emerged from the cell during inspection!)

I didn't see any larva or eggs really, just lots of capped brood (I'd attach a photo if I could!)... so I think (?) that I lost the queen somehow? If I did, wouldn't I have seen supercedure cells at the top of the frame instead of swarm cells at the bottom?

Also....There was still plenty of foundation left to be drawn out. I was under the impression that swarming is generally a hazard when the hive becomes overcrowded. How is that possible when there's still so much foundation left to be drawn?? Or is this just breed instinct? (they are carnolians)

Since I didn't find the queen and didn't see eggs or larva, only capped brood... I left the queen that emerged into the hive as I was inspecting alone and am thinking I'll watch for eggs/larva in 7-10 days or so.

Do they swarm before or after the new queen has emerged?? There's still LOTS Of bees in the hive, would there be noticeably fewer bees today?