Labels not available for Nature in Spreadsheet Editor

In Web UI with nuxeo-spreadsheet installed:

• Navigate to a folder
• Edit the content view to include columns Nature, Coverage and Subjects
• Double-click on a cell under the Nature column, then click again to select a Nature from the dropdown list.
  => None of the Nature labels are available. (see screenshot-1.png)
• Double-click on a cell under the Coverage column, then click again to select a Coverage from the dropdown list.
  => Labels available (see screenshot-2.png)
• Double-click on a cell under the Subjects column, then click again to select a Subject from the dropdown list.
  => Labels available (see screenshot-3.png)

In JSF, all the labels are available.