code: function(){
  					// Maintain the masterButton only when the page is still the current page in detail NavContainer.
  					// If the rerendering occurs after the page navigation, it's not needed to maintain the master button anymore.
  					// This check is needed otherwise it may cause endless rerendering of the last page and the current page.
  					if (!Device.system.phone && (that._oDetailNav.getCurrentPage() === oRealPage)) {
  						if (!oRealPage.getShowNavButton() && that._needShowMasterButton()) {
  							that._setMasterButton(oRealPage, true);
  						} else {
  							that._removeMasterButton(oRealPage);
  						}
  					}
  				}
docs: before rendering is used in order to avoid invalidate in renderer (set button to the header in page)