NSMenuItem displays N/A instead of title

I thought I'd be clever and use a 'dummy' NSMenuItem with a `nil` action and no key equivalent as a title heading in an NSMenu. I have a template NSMenu in IB which I'm populating programmatically with this code:

    let title_item = NSMenuItem.init(title: "Split To:", action: nil, keyEquivalent: "")
    title_item.tag = 100
    title_item.image = split_button
    self.table_menu.addItem(title_item)
    //continue code to add more items

It all displays as expected with the top item showing up as "Split To:", albeit grayed-out

However, when I connect the 'prototype' NSMenu's delegate outlet in IB to my AppDelegate this first item mysteriously becomes "N/A"

The AppDelegate starts with the line:

class AppDelegate: NSObject, NSApplicationDelegate, NSMenuDelegate //...

Could someone tell me a better way to put a title on a contextual menu or what I've done wrong in my current code?

I've also tried adding a menu completely programmatically without IB and the line

self.disk_menu.delegate = self

definitely causes this issue just as it did when graphically connecting it in IB. Maybe it's a bug....