uPortal does a lot of caching, which allows it to scale very well.
Some of the things it caches, however, may change the next time a user authenticates. For this reason, we have a thing called 'UsernameTaggedCacheEntryPurger' that knows how to drop cache entries (portal-wide) that are associated with a username whenever that user logs in.
This thing is (currently) connected with many caches that hold user information. It's not (currently) being applied to the 'org.apereo.portal.groups.GroupMemberImpl.parentGroups' cache, and it needs to be.