Debugger won't show values

[Codex]

I'm using VC++ in Visual Studio 2003 to write a .NET wrapper class
which accesses some unmanaged c code. When debugging, I've noticed
that sometimes the debugger won't show values of unmanaged pointers.
I've reproduced the problem in a VC++ .NET console project. The file
containing the main functions is as follows:

----------------------------------------------------------------

// This is the main project file for VC++ application project
// generated using an Application Wizard.

#include "stdafx.h"
#include <stdio.h>

#using <mscorlib.dll>

using namespace System;

struct TestStruct {
char term[20];
double value[4];
};

int _tmain()
{
// TODO: Please replace the sample code below with your own.
TestStruct *testStruct;
TestStruct *testStruct1;
//TestStruct testStruct2;

testStruct = (TestStruct*)malloc(sizeof(TestStruct));
testStruct->value[0]=0.0;

testStruct1 = new TestStruct();
testStruct1->value[0]=1.7;

//testStruct2.value[0]=1.5;

printf("%f\t%f\n", testStruct->value[0], testStruct1->value[0]);
return 0;
}

----------------------------------------------------------------------------

When setting a breakpoint at the printf statement, the watch window
lists the following for testStruct and testStruct2:
{TestStruct}{term=<undefined value> value=<undefined value>}

I don't get this problem in a Win32 console application, only in .NET.
What might cause this?

Thank you,
codex