Apologies if the Title is not very descriptive but I can't come with any better one right now.
Reference: this Phabricator Query.
For some reason after leaving e.g. Wiki-Setup (as well others) as a member, Phabricator keeps me listed as being a member of its milestones. Considering that milestones cannot have members of their own.
I thought maybe this was caused by some sort of caching or delayed update, but given that it's turning ca. 2 months since that I thought I should file this one so it could be investigated.
For reference I spoke with @mmodell on IRC about this and confirmed me that removals should be immediate so there might be a bug.