Now it's not what I *want*, but it's *consistent*.
The whole time I've been complaining about this, people have been like have you tried an alternate launcher? And I'm like you don't get it, the problem isn't the launcher, the launcher's fine, the problem is the navbar. Except it turns out installing a launcher, by itself, regardless of what the launcher is, "fixes" the problem.
I… *head in hands* Everything about this is so weird. I want the hours I spent trying to debug this with ADB back.