CK is the one creating the .esp and not the game, also, the navmesh didn't make the CK to overload or crash or whatever, but the NPCs would not move ingame.
At the very least it's a CK and game bug.
One part was in the CK, where the navmesh editor was generating bad data. That bug was corrected in CK 1.5.24, and the corresponding fix for the game side was also shipped with 1.5.24. It was only discovered afterward that navmeshes from .esp files were inducing crashes, in what was likely a different area of the code that was overlooked. THAT part of things wasn't fixed until Skyrim 1.6.89.
This issue with the memory limit has no impact on your ability to edit the level, and reporting it as though it does wastes everyone's time worrying about it in the CK. If Bethesda pays attention to this thread, accuracy of reporting is essential. Reporting bugs that only come up on the game side of things doesn't help the CK team one bit.
There is every reason to believe that there are two entirely different groups of people working on this stuff and to have one chase something that will never be reproduced isn't helpful.
Since the vanilla game doesn't have issues with large interiors, it's reasonable to conclude that it handles this better with .esm files. The entire game setup may never have been intended to run things from .esp files at all, which would explain why there have been so many .esp related issues corrected in this engine over the last 12 years.


