Steps to reproduce:

1. Open section Configuration -> Host groups and create host group with names "test".
2. Now, navigate to place where multiselect provides option to select existing host groups and create a new one if needed (host editing form in 4.0 or host mass update form in latest versions). 
3. Try to create a new host group with upper case name "TEST".

Result:
Auto complete doesn't provide option "TEST (new)" because there is already host group with name lowercased "test".
Expected:
Since host groups are case sensitive, multiselect should be able to distinguish "TEST" as new host group.