Login keychain locks itself despite settings saying otherwise?

Since a few days, every so often an app (any app, from Mail to Arq backup) will come up and ask for the login chain password to access basic recurring keychain items like email account passwords.

Usually, keychain issues are resolved with any of these proven recipes: "keychain first aid", "delete and recreate keychain", "make sure login and keychain password are the same", etc — I've tried all those. But, I've been able to isolate some unexpected behavior in Keychain Access: the login keychain gets locked despite settings saying it shouldn't.

Here, you see it locked (it was unlocked half an hour ago):

Yet here are the lock settings:

This is driving me nuts. Any ideas specifically as to why the keychain would be locked?