Steps to reproduce:
1. Create new project
2. Create empty game object and add empty script to it
3. Paste this into the said script:
public enum BuggyEnums {
One,
Two,
//Five,
Three,
Four
}

public BuggyEnums bug;
(Note the commented line)
4. Go to the inspector of the object and select enum value "Three"
5. Open the script again and uncomment line "Five", save the script
6. Open up inspector again for the said object and notice that value is now "Five" instead of "Three"

Actual result: Enum retains its value based on the position of the entry in the list
Expected result: Enum keeps the value it is assigned, regardless of its position

Tested and reproduced on:
Windows 10
Unity 5.2.4p1, 5.3.4p2, 5.4.0b13