clang does not check for assignment of integers to enums

In clang for c/objc, assignment of out-of-range integer values to an enum variable does not raise a warning; whereas use of an out-of-range integer value in a
switch case does raise a warning. This test fails to issue any warning.

typedef enum CCTestEnum
} CCTestEnum;

CCTestEnum foo() {
CCTestEnum test = 3; // no warning
  return 3; // no warning

Is there a reason that his warning is not being issued? On the surface, it looks like a very useful warning.
I am in the process of preparing a patch, which causes this test in clang to issue a warning (test says it should not).
Is there rational for not issuing such warnings?

// From test/Sema/constant-conversion.c
enum Test2 { K_zero, K_one };
enum Test2 test2(enum Test2 *t) {
  *t = 20;
  return 10; // shouldn't warn

- Thanks, Fariborz