I've copied the RENAME icon from the orginal ListerMenu Toolbar to my own toolbar and I all global settings for the toolbars are equal but the copied icon shows the label text.
Looks like you've got Label: Default for both the toolbar (in the Customize dialog) and the individual buttons.
I'm not sure how Opus decides whether to show a label in that case (maybe it's based on other buttons in the toolbar, or a previous setting?) but if you set the individual button label settings to Right or Bottom (or whatever you want) then the labels should appear. Or untick their label boxes if you don't want the label to appear by either button.