Currently it seems that enabling shared settings applies per character, but disabling it applies to all
Or, in more technical terms: when the corresponding flag is disabled in the per character config file it seems to take precedence over the global config file, which then results in the global config being overridden on next logout.

Steps to reproduce:

• Enable shared settings on a character
• Log in and out with another character that did not have shared settings enabled previously OR a character that had it enabled and disabled it before logging out
• Log in with the original character

Result: Shared settings are disabled on the first character that had them enabled originally.

In my opinion this behaviour is inconsistent. It should be either one of the two:

• Shared settings get enabled/disabled for all characters whenever you change it in the option menu
• Shared settings get enabled/disabled per character

Currently I worked around this behaviour by having logged through all my characters and enabling the setting. However if I were to create a new character I'd also need to remember to do this before logging out for the first time.