Suppress blank namespace in XML element

I have an XML element I am creating. I want Xmlns information to appear in the parent element but no references in any child elements. To acheive this, I am using the following code:

XNamespace xsi = "http://ift.tt/ra1lAU";
XNamespace xsd = "http://ift.tt/tphNwY";
XNamespace xns = "http://ift.tt/1CsVxqW";
var xroot = new XElement(xns + "Constraints", new XAttribute(XNamespace.Xmlns + "xsd", xsd.NamespaceName), new XAttribute(XNamespace.Xmlns + "xsi", xsi.NamespaceName));
var keyElement = new XElement("Keys");
var kElement = new XElement("K");
kElement.Value = "HDD";
keyElement.Add(kElement);
xroot.Add(keyElement);
xroot.Add(new XElement("Properties"));
xroot.Add(new XElement("MustIncludeKeys"));

What I am getting is:

<Constraints xmlns:xsd="http://ift.tt/tphNwY" xmlns:xsi="http://ift.tt/ra1lAU" xmlns="http://ift.tt/1CsVxqW">
  <Keys xmlns="">
    <K>HDD</K>
  </Keys>
  <Properties xmlns="" />
  <MustIncludeKeys xmlns="" />
</Constraints>

What I want is:

<Constraints xmlns:xsd="http://ift.tt/tphNwY" xmlns:xsi="http://ift.tt/ra1lAU" xmlns="http://ift.tt/1CsVxqW">
  <Keys>
    <K>HDD</K>
  </Keys>
  <Properties />
  <MustIncludeKeys />
</Constraints>

What can I do to get rid of the extraneous (blank) name spaces "xmlns="" "? I've tried keyElement.ReplaceAttributes("") and even tried using the System.Xml namespace to use the RemoveAttribute Method - to no avail.