User removed from group upon login if case of group name differs in Crowd User Directory

To reproduce:

1. Set up Confluence with a Crowd User Directory
2. Create a group with a lower case name in the Confluence Internal directory
3. Create a group in the associated Crowd directory with the same name except with a case difference
4. Add the user to the group in Crowd
5. Synchronize the User Directory
6. View the user's group membership in Confluence - the user will be in the group
7. Log the user into Confluence
8. View the user's group membership in Confluence - the user will be removed from the group