Comment 1 for bug 907792

Currently it seems that the actual number of available screens affects the behaviour:

(core/ui/maindisplay.py)

        if self.isLive:
            if self.hideMode:
                self.hideDisplay(self.hideMode)
            else:
                # Single screen active
                if self.screens.display_count == 1:
                    # Only make visible if setting enabled
                    if QtCore.QSettings().value(u'general/display on monitor',
                        QtCore.QVariant(True)).toBool():
                        self.setVisible(True)
                else:
                    self.setVisible(True)