Cannot select multiple layouts in Tab Layout Widget Editor

When defining which layouts to display in a custom Tab (toggleable), and despite that the tooltip says it should be possible to select more than one layout in both the 'before' and 'after' toggle mode, I am unable to do so. It is neither possible to select multiple layouts from the pop-up dialog that lists them all, nor to manually type in a "list of multiple layout names, separated by commas" as the tooltip suggests.