Consider this input code:
---
public enum BrokenEnum {
    A,
    void t() {}
    B;
}
---

When compiled, this leads to these errors:
---
$ javac BrokenEnum.java
BrokenEnum.java:2: error: <identifier> expected
    A,
      ^
BrokenEnum.java:3: error: ',', '}', or ';' expected
    void t() {}
    ^
BrokenEnum.java:3: error: '}' expected
    void t() {}
        ^
BrokenEnum.java:5: error: class, interface, or enum expected
}
^
4 errors
---

And the AST is:
---
public enum BrokenEnum {
    /*public static final*/ A /* = new BrokenEnum() */ /*enum*/ ,
    /*public static final*/ <error> /* = new BrokenEnum() */ /*enum*/ ;
    (ERROR)
}(ERROR)
---

Both of these are fairly inconvenient.