Deployment of SharePoint navigation items using the provisioning engine ignored

We are deploying site structure using a PnP provisioning template to the root of SharePoint site collections using the PnP Provisioning framework. Everything gets deployed except navigation items.

I've narrowed the situation down to a small provisioning script with only Security and Navigation elements. When I deploy this, the security element is picked up by the provisioning engine, but the navigation element not.

Why is this not working?

<?xml version="1.0"?>
<pnp:Provisioning xmlns:pnp="http://schemas.dev.office.com/PnP/2016/05/ProvisioningSchema">
  <pnp:Preferences Generator="OfficeDevPnP.Core, Version=2.6.1608.0, Culture=neutral, PublicKeyToken=3751622786b357c2" />
  <pnp:Templates ID="CONTAINER-TEMPLATE-7FB72622E1654B1C9765678E8C5093A3">
    <pnp:ProvisioningTemplate ID="TEMPLATE-7FB72622E1654B1C9765678E8C5093A3" Version="1" BaseSiteTemplate="STS#0">
      <pnp:Security ClearSubscopes="false">
        <pnp:AdditionalOwners>
          <pnp:User Name="c:0-.f|rolemanager|spo-grid-all-users/9fcc7bfd-834f-4f72-89f1-509ad9e9a92f" />
        </pnp:AdditionalOwners>
      </pnp:Security>
      <pnp:Navigation>
        <pnp:GlobalNavigation NavigationType="Structural">
          <pnp:StructuralNavigation RemoveExistingNodes="true">
            <pnp:NavigationNode IsExternal="true" Title="Wikipedia" Url="http://www.wikipedia.org"></pnp:NavigationNode>
          </pnp:StructuralNavigation>
        </pnp:GlobalNavigation>
        <pnp:CurrentNavigation NavigationType="Structural">
          <pnp:StructuralNavigation RemoveExistingNodes="true">
            <pnp:NavigationNode IsExternal="false" Title="Start" Url="/SitePages/Home.aspx"></pnp:NavigationNode>
            <pnp:NavigationNode IsExternal="false" Title="Project team" Url="{site}">
              <pnp:NavigationNode IsExternal="false" Title="Work docs" Url="{site}/Work documents"></pnp:NavigationNode>
              <pnp:NavigationNode IsExternal="false" Title="Mail" Url="{site}/Work mail"></pnp:NavigationNode>
              <pnp:NavigationNode IsExternal="false" Title="Deliverables" Url="{site}/Deliverables"></pnp:NavigationNode>
            </pnp:NavigationNode>
            <pnp:NavigationNode IsExternal="true" Title="Wikipedia" Url="http://www.wikipedia.org"></pnp:NavigationNode>
          </pnp:StructuralNavigation>
        </pnp:CurrentNavigation>
      </pnp:Navigation>
    </pnp:ProvisioningTemplate>
  </pnp:Templates>
</pnp:Provisioning>

I've managed to deploy the navigation items as a workaround using the PnP PowerShell august 2016 cmdlets using the Add-SPONavigationNode method, but I would like to transform this into a provisioning template.