Beth is too busy with a vision of people yelling FUS RO DAH at their TVs while we have the vision of an NPC just standing there with broken NavMesh unfortunatly.

LOL. It sure does seem that way sometimes, doesn't it?

They have enough people to do both. I'm hoping the lack of comments on their part just means that they're still working on it and have nothing new to say.
sooo, i think this is too much of a coincidence.
ive been combing and picking apart the NAVI entries, and it seems that any time you create a new navmesh, it always has the same NVMI entries no matter what.
Helgen Exterior
Whiterun Exterior
Windhelm Exterior
Dawnstar... etc
Sound familiar?
This would be expected actually. The NAVI record is global in scope and contains information on every navmesh in the game, including the ones you're adding to it. The game takes the NAVI data from every mod that has it and merges it into one record internally. If it didn't, then all it would take to spoil everyone's navmeshes everywhere would be one mod that changes one and is loaded last.
I think it would be pretty interesting though if you've found some correlation between how the NAVI record is assembled and merged with mod data and the resulting missing interiors in various places that have been modded. My alt-start mod does indeed add two fresh new cells to the game, both have navmeshes, and I've seen reports of the Helgen cave and the DB sanctuary outside Falkreath disappearing. It's left me to wonder if some of this is because people are refusing to include Update.esm as one of their masters. I always do, but plenty of other modders don't. An inconsistency in master data could definitely throw wrenches into things.
One thing you should not do though is start hacking data out of the NAVI record. It's intended to be there. Having it go missing will just end up breaking door links or something.
Regarding my Riften tests: I did more with it and found yet even stranger happenings. Some instances of NavMesh could be fixed by the aforementioned 'merging into Vanilla' technique... BUT some of the 'cured' cells still have actors' AI broken. This doesn't happen all the time, but it does happen in the same cell each time it DOES (which is NOT the Anathema Cell of yore, stranger yet even).
You're aware that the currently released copy of Open Cities already has vanilla merged navmeshes, right?
@RealmEleven: Oblivion uses the path grid system. The only thing related to that which doesn't work properly, IIRC is auto-generate. You have to do all the pathing manually. At this point, I'd rather work with path grids.
Even the auto-generate works so long as you don't attempt it on more than individual cells. Trying to do that over regions or entire worldspaces is asking for the CS to crash due to memory overload.
Also, yes, I'd be the happiest person on Earth if path grids came back and navmeshes were burned at the stake. I can path grid an entire city in under an hour and have it work the first time and never look back.
So why does that subrecord change if nothing's different in the cell? Even though the navMesh hasn't changed whatsoever, why does finalizing an adjacent cell change THIS cell's data?
It has to in order to update the edge connection data.