Isolate.WhenCalled mocks extra properties

Hello,
I have 1 issue with type data set when I pass to method typed datarow value and try to mock such a call. e.g.:

Isolate.WhenCalled( () => someObj.Do(typedDataRow.FooTypedProperty)).IgnoreCall();

FooTypedProperty property has been mocked as well as Do method call and returns null when I try to read its value.

I was able to reproduce issue (or may be this is expected behavior?) in example below:
1. Classes definition:

public class FooClass
{
    public void Do(string input)
    {
        //do some task
    }
}

public class SubFooClass
{
    public string Value { get; set; }
}

2. Tests:

[TestMethod]
[Isolated]
public void IsItValidMockTest()
{
    //expectations
    string expected = "faked value";
    //prepare
    FooClass foo = new FooClass();
    SubFooClass subFoo = new SubFooClass() { Value = expected };
    Isolate.WhenCalled(() => foo.Do(subFoo.Value)).IgnoreCall();
    //run
    foo.Do(subFoo.Value);
    //assertations
    Assert.AreEqual(expected, subFoo.Value); //assertation fails. value is null
    Isolate.Verify.WasCalledWithExactArguments(() => foo.Do(subFoo.Value)); //verification fails. method wasn't called
}

More over when I try to make sure that Do is called with exact arguments I get the following error:
"*** Cannot mock types from mscorlib assembly."

[TestMethod]
[Isolated]
public void IsItValidMockTestAnother()
{
    //expectations
    string expected = "faked value";
    //prepare
    FooClass foo = new FooClass();
    SubFooClass subFoo = new SubFooClass() { Value = expected };
    Isolate.WhenCalled(() => foo.Do(subFoo.Value)).WithExactArguments().IgnoreCall(); //fails with "*** Cannot mock types from mscorlib assembly."
    //run
    foo.Do(subFoo.Value);
    //assertations
    Assert.AreEqual(expected, subFoo.Value);
    Isolate.Verify.WasCalledWithExactArguments(() => foo.Do(subFoo.Value));
}

Is it expected behavior? If yes then how should I mock such a method call?

TIA,
Grammer