compiler warnung #66-D: enumeration value is out of "int" range

Hello,
I'm getting many of this warning in my project which uses NXP header with enum definitions similat to this:

typedef enum _clock_attach_id
{
  kFRO12M_to_MAIN_CLK = MUX_A(CM_MAINCLKSELA, 0) | MUX_B(CM_MAINCLKSELB, 0),
  kNONE_to_NONE = 0x80000000UL,
} clock_attach_id_t;

The warning seems to be obvious because 0x80000000UL does not fit into int.

But the compiler manual v5.06 for µVision says about enum:

10.4 Structures, unions, enumeratons and bitfields in ARM C and C++

In C mode, and in C++ mode without --enum_is_int, if an enum contains only positive enumerator values, the storage type of the enum is the first unsigned type from the following list, according to the range of the enumerators in the enum. In other modes, and in cases where an enum contains any negative enumerator values, the storage type of the enum is the first of the following, according to the range of the
enumerators in the enum:
• unsigned char if not using --enum_is_int
• signed char if not using --enum_is_int
• unsigned short if not using --enum_is_int
• signed short if not using --enum_is_int
• signed int
• unsigned int except C with --strict
• signed long long except C with --strict
• unsigned long long except C with --strict

Maybe I misinterpret this, but I would think the compiler should choose "unsigned int" in this case. If so, why is there the warning?

The code works as expected, but I would like to minimize the number of warnings in the project (without code modification). Disableing this warning is also not good because it might hide a "real" problem.

Regards, Gunnar