Woops, that basement statement was literally meant to say foundation since that was something I saw done in a CFE tutorial...place a foundation with wall on it, then delete foundation and put wall under it. I changed it in my post. No clue if CFE and basements have anything to do with one another :0
The routing system is totally different from past games as well and is something I don't know too much about. In general we were more allowing with clipping between Sims to reduce the chance of route issues, which is one reason they route much better...but there is also a ton of awesome tech making it way better. From what an engineer tells me though, stairs are still portals, but the foundation thing is a special piece of code we added just to make that work....I believe because our world builders had built some houses that looked like you should be able to walk into them, but it turned out you couldn't. That was clearly bad so we fixed it.
On the bug thing, we have a team that tries to keep an eye on all the forums and collect issues/bugs reported by players. I believe Crinrict just does a really good job of outreach to the community and asks for a lot of useful details so we keep an extra eye on that thread. But that whole forum is devoted to people reporting bugs.