Steps to reproduce:
1. Download and open attached project "Duplicate Enums.zip"
2. Attach script "Script1" to any game object in the same
3. In the attached object's inspector view, script's component there are two field
4. For the bottom one, "Enum Value", choose "Value 0" and notice console output - "Value0 (0/0)" (Enum named constant (Enum value/Enum index))
5. Select "Value 1_1" and notice output - "Value1_1(1/1)"
6. Select "Value 1_2" and notice that output is the same as for "Value 1_1" and named constant has not been changed in inspector/editor

Expected result: Regardless of chosen enum value, named constant is changed if it is different

Tested and reproduced:
Windows 10
Unity 5.1.4f1, 5.2.4p1, 5.3.3p3, 5.4.0b9