Why did I have to use an int to combine these enum flag values together?

Question

Perhaps someone can just explain the logic behind why this is actually an issue.

In my C# DLL I have a set of flag values that expose via the COM API:

[Flags]
[Guid("~~~")]
[ComVisible(true)]
public enum AssignmentType
{
    None = 0,
    Attendant = 1,
    ConductorCBS = 2,
    ReaderCBS = 4,
    Chairman = 8,
    Mike = 16,
    PlatformAttendant = 32,
    Prayer = 64,
    OCLM = 128,
    Sound = 256,
    Student = 512,
    Custom = 1024,
    Demonstration = 2048,
    Assistant = 4096,
    Host = 8192,
    CoHost = 16384,
    OCLMTreasures = 32768,
    OCLMGems = 65536,
    OCLMLiving = 131072,
    StudentBibleReading = 262144,
    StudentDiscussion = 524288,
    StudentTalk = 1048576
}

In my C++ MFC project, the above is exposed as follows:

enum __declspec(uuid("~~~"))
AssignmentType
{
    AssignmentType_None = 0,
    AssignmentType_Attendant = 1,
    AssignmentType_ConductorCBS = 2,
    AssignmentType_ReaderCBS = 4,
    AssignmentType_Chairman = 8,
    AssignmentType_Mike = 16,
    AssignmentType_PlatformAttendant = 32,
    AssignmentType_Prayer = 64,
    AssignmentType_OCLM = 128,
    AssignmentType_Sound = 256,
    AssignmentType_Student = 512,
    AssignmentType_Custom = 1024,
    AssignmentType_Demonstration = 2048,
    AssignmentType_Assistant = 4096,
    AssignmentType_Host = 8192,
    AssignmentType_CoHost = 16384,
    AssignmentType_OCLMTreasures = 32768,
    AssignmentType_OCLMGems = 65536,
    AssignmentType_OCLMLiving = 131072,
    AssignmentType_StudentBibleReading = 262144,
    AssignmentType_StudentDiscussion = 524288,
    AssignmentType_StudentTalk = 1048576
};

This is the part of don't get:

int iFlag = MSAToolsLibrary::AssignmentType::AssignmentType_None;
for (int iIndex = 0; iIndex < m_lbAssignmentsOCLM.GetCount(); iIndex++)
{
    if (m_lbAssignmentsOCLM.GetCheck(iIndex) == BST_CHECKED)
    {
        iFlag |= static_cast<MSAToolsLibrary::AssignmentType>(m_lbAssignmentsOCLM.GetItemData(iIndex));;
    }

}
theApp.WriteProfileInt(
    theApp.GetActiveScheduleSection(_T("Options")), _T("SRR_AssignmentsOCLM"), iFlag);

I had to use int for the iFlag variable. If I try to make that variable a MSAToolsLibrary::AssignmentType then the |= line will not work.

Yet, I am able to make calls like this to the API:

const COleDateTime datMeeting = GetMeetingDate(iRow);
auto eTypesToInclude = static_cast<MSAToolsLibrary::AssignmentType>(GetAssignmentsOCLMFlag());
CStringArray aryStrMeetingPersonnel;
theApp.MSAToolsInterface().GetPersonnelForMeeting(
    datMeeting,
    theApp.GetAssignHistoryPathEx(), 
    eTypesToInclude, aryStrMeetingPersonnel);

In short, why is it OK to pass the combined flag values as a MSAToolsLibrary::AssignmentType to a function in the API, but I had to use an int to build the compiled flags value first.

Make sense?