when an element is selected from the app structure panel, if we press DEL button on keyboard, the item does not get deleted, we have to click the element in design view and only then the DEL button will delete the element.
in this attached image, navbra brand is selected but not deleteable by DEL button, have to either click the X in th aPp Structure menu above or select the element from the design view and then press DEL.
hope we have explained the request properly.