[Bug] Changing game setting breaks Dark Brotherhood quest

The stat increase you get on level up is controlled by the game setting iAVDhmsLevelUp. The vanilla value is 10, but if you set it to 8 or lower the Dark Brotherhood questline fails to initialize (e.g. you can't talk to the black door). I have no idea why this should happen, as that game setting has nothing to do with the DB questline. But I can recreate it easily:

1. Set iAVDhmsLevelUp to 8 or lower (here's a plugin to do it if you want).
2. Start a new game and wait about 10 seconds.
3. Type "sqv darkbrotherhood" in the console. Note that all the quest aliases are missing their values and the quest stage stays stuck at 0 instead of getting to 1.

For comparison, try setting iAVDhmsLevelUp to other values. 0-8 are all broken for me, but 9 and 10 work fine.

Does anyone have any idea what's causing this? Are you able to reproduce it on your end?