umdh.exe shows only a fraction of allocations for a specific stack

Question

I'm trying to learn how to troubleshoot memory leaks with umdh.exe. In order to do it I wrote a sample app:

void MemoryLeakTest(int argc, _TCHAR* argv[]);

int _tmain(int argc, _TCHAR* argv[])
{
    MemoryLeakTest(argc, argv);
    return 0;
}

void MemoryLeakTest(int argc, _TCHAR* argv[])
{
    if (argc != 3)
    {
        wcout << "HelloWorld.exe <number of allocations> <number of bytes>" << endl;
        getchar();
        return;
    }

    int numAllocations = _wtoi(argv[1]);
    int numBytes = _wtoi(argv[2]);

    wcout << "Num allocations: " << numAllocations << ", num bytes: " << numBytes << endl;
    wcout << "Press any key to start..." << endl; 
    getchar();

    for (int i = 0; i < numAllocations; ++i)
    {
        void* unusedMemory = new byte[numBytes];

        if ((i % (numAllocations / 100)) == 0)
        {
            wcout << i << endl;
            Sleep(100);
        }
    }

    wcout << "Press any key to finish..." << endl;
    getchar();
}

Compiled (release), configured umdh.exe:

1. set _NT_SYMBOL_PATH=http://msdl.microsoft.com/symbols/download;C:\TestProjects\HelloWorld\x64\Release;
2. gflags.exe /i HelloWorld.exe +ust

Then did the experiment:

1. HelloWorld.exe 10000 1000
2. Waited till it stops @ first getchar
3. umdh.exe -pn:helloworld.exe -f:c:\first.log
4. Continued execution, waited till it stops @ second getchar
5. umdh.exe -pn:helloworld.exe -f:c:\second.log

What I noticed is that no matter with which parameters I call, whether it is 100 allocations or 1000 allocations, first.log and second.log look very similar (for different experiments).

6. umdh.exe -d c:\first.log c:\second.log -f:c:\result.log

And then I get the only stack with only 17 allocs (instead of expected 1000):

+   17000 (  17000 -      0)     17 allocs  BackTraceB5023D4D
+      17 (     17 -      0)    BackTraceB5023D4D   allocations

ntdll!memset+165B9
MSVCR120!malloc+5B
MSVCR120!operator new+1F
HelloWorld!MemoryLeakTest+108 (c:\my\main\private\testproject\debugit\helloworld\helloworld.cpp, 40)
HelloWorld!wmain+9 (c:\my\main\private\testproject\debugit\helloworld\helloworld.cpp, 16)
HelloWorld!__tmainCRTStartup+10F (f:\dd\vctools\crt\crtw32\dllstuff\crtexe.c, 623)
KERNEL32!BaseThreadInitThunk+D
ntdll!RtlUserThreadStart+1D

UPDATED: TaskProcess shows that both private bytes and commit size grow on expected value.

UPDATED2: DebugDiag shows a leak correctly with 10000 allocations and a few sampled call stacks pointing to right location.

Any idea what I'm doing wrong?

Thank you!