Problem with defining Site Columns in a feature

Question

Why the titles are blank (for example, I go to setting, site columns and select the group. I see all four columns but their title are missing. like, pobox, firstclassdate, deliverytype, carrier) for the site columns created with feature?

This is === feature.xml ===

<Feature Id="{10474c0f-7474-49f6-0147-d43d3d02037f}" 
  Title="Custom Site Columns" 
  Description="Columns Description" 
  Version="1.0.0.0" 
  Scope="Site" 
  xmlns="http://schemas.microsoft.com/sharepoint/">
  <ElementManifests>
    <ElementManifest Location="elements.xml" />
  </ElementManifests>
</Feature>

This is === elements.xml ===

<?xml version="1.0"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
  <Field Type="Text" 
         Required="FALSE" 
         MaxLength="255" 
         Group="Toshiba Site Columns" 
         ID="{50eece5f-a323-4d1f-8e6a-a661fac980f6}" 
         Name="POBOX" 
         DisplayName="P. O. Box"                 
         StaticName="POBOX" 
         xmlns="http://schemas.microsoft.com/sharepoint/">
  </Field>
  <Field Type="DateTime" 
         Required="FALSE" 
         Format="DateTime" 
         Group="Toshiba Site Columns" 
         ID="{d08e789c-0b0a-4779-ab1c-32ab4ca6b2c3}"        
         Name="FirstClassDate"
         DisplayName="First Class Mail Date"
         StaticName="FirstClassDate"  
         xmlns="http://schemas.microsoft.com/sharepoint/">
  </Field>
  <Field Type="Text" Required="FALSE" MaxLength="255" Group="Toshiba Site Columns" ID="{9834a3a3-9752-47e7-b186-9273e8f92624}" Name="Carrier"  DisplayName="Carrier Type" StaticName="Carrier"  xmlns="http://schemas.microsoft.com/sharepoint/">
  </Field>
  <Field Type="Text" Required="FALSE" MaxLength="255" Group="Toshiba Site Columns" ID="{91a39fdb-3417-41e1-81aa-bf989bff000e}" Name="DeliveryType" DisplayName="Delivery Type Regular Overnight" StaticName="DeliveryType"  xmlns="http://schemas.microsoft.com/sharepoint/">
  </Field>
</Elements>

Answer 1

Based on the xml provided (thanks Anders!) I created the feature and everything seems to work as expected. Under site columns I see the following:-

Each of the columns appears and is linked so that you can edit them. Is this not what you see?