Balance expanding to fill available space. Polish expanding to fill unavailable space that you'd swear you thought you wouldn't be using. Resource hassles before we got our pipeline working better... We'll do a postmortem all right, I'm just not sure what it would say on this topic though - it's probably mostly due to the beta meaning that we have loads of player feedback, so it almost feels like the game IS out to us in some respects. We know it's not done, which is why we've been seriously changing focus in the last few months.
Another large part of it could be that we come from a rapid prototyping perspective, so we got the "game" part up and running really quickly, there wasn't a lot of wasted time writing engine elements, etc. So at the moment the game tends to look relatively static, while under the skin large systems that are needed for achievements or edge cases in saving and loading are being added all the time. Dungeon restarting is a seriously complex thing, for instance.