title: 'DefaultValue' property was already registered by 'Xceed_Wpf_Toolkit_NumericUpDown`1_12_151463089'
body: <h1>Error Description</h1>
  
  <p>I've searched for this error but every other topic was involving C# code and metadata/dependency overridings.</p>
  
  <p>But my problem actually involves only and just XAML declarations (of course, it has "MyControl.xaml" and "MyControl.xaml.cs", but nothing that even mention any control that gives those errors).</p>
  
  <p>Also, it <strong>does</strong> compile, the program runs OK, everything is fine, but it gives a build error (tracked in blue) is annoying to see every line envolving <em>xctk</em> underlined in blue as if it had something wrong.</p>
  
  <p>If I do:</p>
  
  <pre><code>&lt;xctk:IntegerUpDown /&gt;
  </code></pre>
  
  <p>I get this:</p>
  
  <blockquote>
    <p>'DefaultValue' property was already registered by 'Xceed_Wpf_Toolkit_NumericUpDown'1_12_151463089'</p>
  </blockquote>
  
  <h1>How to reproduce</h1>
  
  <p>Just do anything envolving Xceed WPF Toolkit:</p>
  
  <pre><code>&lt;xctk:DecimalUpDown /&gt;
  &lt;xctk:IntegerUpDown x:Name="something" /&gt;
  &lt;xctk:IntegerUpDown Name="something" /&gt;
  &lt;xctk:IntegerUpDown DefaultValue="0" /&gt;
  &lt;xctk:IntegerUpDown x:Name="something" DefaultValue="0" /&gt;
  </code></pre>
  
  <p>No aditional C# code involved, still all of above gives the same error.</p>
  
  <h1>Aditional Information</h1>
  
  <p>"xctk" is defined this way in my UserControl XAML:</p>
  
  <pre><code>&lt;UserControl
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      ...other definitions...
      xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"
  </code></pre>
  
  <p>What could it be related with and what should I check first?</p>
  
  <p>(EDIT)</p>
  
  <h1>More Aditional Information</h1>
  
  <p>Just found that DoubleUpDown doesn't raise the error:</p>
  
  <p><code>&lt;xctk:DoubleUpDown /&gt;</code></p>