can access resource library from main .exe but not loaded .dll

I have a library MyLib.dll, which I am testing via a test program
TestProgram.exe.
TestProgram.exe is an ATL app which statically links to MyLib.dll.

MyLib.dll requires some resources in MyRes.dll, so, before calling any
routines in MyLib.dll, TestProgram.exe first loads the MyRes.dll
resource library.

The code to do so:

****************** CODE START ******************

static LPCTSTR gsResourceDLL = _T("MyRes.dll");
HRESULT CMainDlg::LoadResourceDLL()
{
    // Load Resource DLL
    TCHAR lpszLocFileName[_MAX_PATH];
    GetModuleFileName( _AtlBaseModule.GetModuleInstance(),
lpszLocFileName, _MAX_PATH);
    PathRemoveFileSpec(lpszLocFileName);
    _tcscat( lpszLocFileName, _T("\\") );
    _tcscat( lpszLocFileName, gsResourceDLL);

    HMODULE hm = LoadLibrary( lpszLocFileName );

    if ( hm == 0 )
    {
        return S_FALSE;
    }

    HINSTANCE hThisModule = _AtlBaseModule.GetModuleInstance();
    _AtlBaseModule.AddResourceInstance(hm);

    return S_OK;
}

****************** CODE END ******************

I can verify that the library is correctly loaded via the following
test routine, which just attempts to find and lock a particular
resource in the resource library:

****************** CODE START ******************

void TestResource(LPCTSTR lpszResourceName)
{
    LPVOID lpResource = NULL;
    HGLOBAL hResource = NULL;
    HRSRC hDlgInit = NULL;

    int i = 0;
    HINSTANCE hInst = _AtlBaseModule.GetHInstanceAt(i);
    while(hInst != NULL)
    {
        WORD wLanguage = 0;
        hDlgInit = ::FindResourceEx(hInst, RT_HTML,
ATL::CW2CT(lpszResourceName), wLanguage);
        if (hDlgInit != NULL)
            break;

        //get next
        hInst = _AtlBaseModule.GetHInstanceAt(i++);
    }

    if (hDlgInit != NULL)
    {
        // load it
        hResource = ::LoadResource(hInst, hDlgInit);
        if (hResource == NULL)
            return;

        // lock it
        lpResource = ::LockResource(hResource);
        _ASSERT(lpResource != NULL);
    }

    //do something with the resource...

    // cleanup
    if (lpResource != NULL && hResource != NULL)
    {
        UnlockResource(hResource);
        FreeResource(hResource);
    }
}

****************** CODE START ******************

However, when MyLib.dll tries to access the same resource in the exact
same way, it fails to find it (FindResourceEx never finds anything and
always returns NULL).

What is going on?

If I add the load library code to MyLib.dll and run it from
TestProgram.exe, then MyLib.dll can find resources in MyRes.dll...

Why is this necessary? Why can't MyRes.dll see resources loaded by and
available to TestProgram.exe? They use the same handles for the
resource as far as I can tell...

Thanks in advance for any help you can provide.