PageHeader should not have a back action if it's the first page on the stack

Confirmed with this program:

import QtQuick 2.4
import Ubuntu.Components 1.3

MainView {
    width: units.gu(50)
    height: units.gu(60)

    PageStack {
        Component.onCompleted: push(p1)
        Page {
            id: p1
            header: PageHeader {
                title: i18n.tr("untitled21")
            }
        }
    }
}

I could not reproduce the issue with the AdaptivePageLayout.

This bug was fixed in the package ubuntu-ui-toolkit 1.3.1938+15.04.20160412 in https://launchpad.net/~ci-train-ppa-service/+archive/ubuntu/stable-phone-overlay

---------------

ubuntu-ui-toolkit (1.3.1938+15.04.20160412) vivid; urgency=medium

  [ Tim Peeters ]
  * Hide the PageStack back button when depth == 1. Fixes LP: #1565811
  * Add header subtitle. Fixes LP: #1399289
  * Reveal the header in gallery when changing the layout to two columns.
    Fixes LP: #1556860
  * Set correct colors for disabled actions in the header.
    Fixes LP: #1393485
  * Disable tst_datepicker.qml to unblock the staging.Fixes LP: #1567840
  * Prevent invisible header from setting the flickable topMargin.
    Fixes LP: #1560419, LP: #1560458, LP: #1566231.

  [ Zsombor Egri ]
  * Move MouseTouchAdaptor into UbuntuToolkit library. Fix adaptor code for
    Xenial. Fixes LP: #1561436

  [ Christian Dywan ]
  * Don't use a separate argument to distinguish touch events. If it's touch,
    it has our overloaded methods. Fixes LP: #1530802
  * Use export_qml_dir.sh in qmlapicheck and runtest Also add Usage to runtest.
    Fixes LP: #1567286.
  * Summary style error results with sections. Fixes LP: #1568804

  [ Andrea Bernabei ]
  * Mouse filter: check if mouse is inside the area on mouse moves and
    setHovered accordingly. Fixes LP: #1566378.

  [ Timo Jyrinki ]
  * Add latest changes for GLES.
  * Add back Provides: qtdeclarative5-ubuntu-ui-toolkit-plugin to resolve
    upgrade issue. Fixes LP: #1568817
  * Fix wrapper script auto-generated by Qt that incorrectly tries to execute
    itself. Fixes LP: #1560000
  * bileto_convert_to_gles: sort and add
    qml-module-ubuntu-performancemetrics-gles.install. Fixes LP: #1569217

  * Add additional Breaks as requested by archive admin.
  * Add latest changes for GLES.

  [ Zolán Balogh ]
  * Fix the UITK test plan script.

  [ CI Train Bot ]
  * Resync trunk. added: examples/ubuntu-ui-toolkit-gallery/po/nb.po

  [ Robert Park ]
  * Inline GLES packaging. added: debian/bileto_convert_to_gles
    debian/control.gles debian/rules.gles

 -- Zoltan Balogh <email address hidden> Tue, 12 Apr 2016 11:12:44 +0000

This bug was fixed in the package ubuntu-ui-toolkit - 1.3.1984+16.10.20160527.2

---------------
ubuntu-ui-toolkit (1.3.1984+16.10.20160527.2) yakkety; urgency=medium

  [ Christian Dywan ]
  * Slimmer frame for TextFields: 0.5dp. Fixes LP: #1578190.

  [ Albert Astals Cid ]
  * Add override
    The override specifier (since C++11) specifies that a virtual function
    overrides another virtual function. In a member function declaration or
    definition, override ensures that the function is virtual and is overriding
    a virtual function from the base class.

  [ Tim Peeters ]
  * Fix reference error in PullToRefreshStyle. Fixes LP: #1582843
  * Mark Tab, Tabs, TabBar, PageHeadConfiguration, PageHeadSections,
    PageHeadState, ToolbarButton, ToolbarItems as deprecated in the
    documentation. Fixes LP: #1566735, LP: #1566741.

  [ CI Train Bot ]
  * Resync trunk.

 -- Zoltan Balogh <email address hidden> Fri, 27 May 2016 07:08:44 +0000