I changed my WaniKani password on another computer, while I was logged into the service on this machine. Now, I notice that, although my https://wanikani.com session has been invalidated on this computer (as I expected it to happen), the forum session has not been invalidated, and I can post normally, even though I have not logged in with the new credentials yet.
That would be an issue with the Discourse side, でしょう ?
I found this topic from a few years ago where someone mentioned that error:
And then something about fixing it here…
…but considering you’re still having the issue… 
That’s all I’ve got 
Well, you do not change the password via discourse, but by using the WK interface. So perhaps this patch has no effect in this situation
I don’t even think you can change the password using discourse
Ooo gotcha, yeah I don’t think you can, then it’s probably an issue between WK → Discourse
Yeah, I think it is our end that would be responsible to invalidate the forum session. The boards are on a SSO with your WK login. I’ll look into this.
Thanks. 
Just in case anyone is interested…