Steps to Reproduce:

• Create a number of Groups with mixed cases
• Preview the People/Roles section of any project administration
• Attempt to add a group to any Project Role by typing into the Group's field
• The behaviour of the Group browser field can be quite erratic as shown in the attached screenshots. Basically the field will sometimes behave as case-insensitive.

Screenshot:

• case-insensitive behaviour after entering 1 character
  

• case sensitive behaviour after entering 2 characters
  

Notes
It is good to note that while it is not possible to create a group like 'Jira-users' (it will not be created due to this bug), it can still be created via import. When both 'Jira-users' and 'jira-users' exist on the instance, attempts to remove 'Jira-users' will instead remove 'jira-users'.