Document Protection with OpenXML SDK 2

Question

I am programmatically creating a DOCX file using OpenXML SDK v2. One of the requirements of the document is it be protected to avoid editing.

This is accomplished using the DocumentProtection object like:

new DocumentProtection
{
    Edit = DocumentProtectionValues.ReadOnly,
    Enforcement = BooleanValues.One,
    CryptographicProviderType = CryptProviderValues.RsaFull,
    CryptographicAlgorithmClass = CryptAlgorithmClassValues.Hash,
    CryptographicAlgorithmType = CryptAlgorithmValues.TypeAny,
    CryptographicAlgorithmSid = 4,
    CryptographicSpinCount = 50000,
    Hash = hash,
    Salt = salt
}

This works beautifully when the document is opened in Word 2007, but when opened in Word 2003 with the compatibility pack the protection can be removed without entering a password.

Reading online this appears 'by design' or at least expected.

Does anyone have any clever ideas on keeping the password protection in-tact when viewed within Word 2003?