Consider the following code:
---
enum EnumSwitch {
    A, B;
    public static int c(EnumSwitch e) {
        switch (e) {
            case EnumSwitch.A: return 1;
            case EnumSwitch.B: return 2;
        }
    }
}
---

Compiling this will produce these three errors:
---
EnumSwitch.java:5: error: an enum switch case label must be the unqualified name of an enumeration constant
            case EnumSwitch.A: return 1;
                           ^
EnumSwitch.java:6: error: an enum switch case label must be the unqualified name of an enumeration constant
            case EnumSwitch.B: return 2;
                           ^
EnumSwitch.java:6: error: duplicate case label
            case EnumSwitch.B: return 2;
            ^
3 errors
---

The first two errors are appropriate, but the third one is not: there is no duplication in the labels.

This has originally been filed as part of JDK-8048805.