Toolbar in main VC and Toolbar in Modal VC won't show same button

Toolbar in main VC and Toolbar in Modal VC won't show same button

I am running into a weird issue that I can't find anything for on the
internet. I have a UIViewController that is showing a toolbar at the
bottom with a custom button in it. That button is added like..
List<UIBarButtonItem> items = new List<UIBarButtonItem>();
UIButton _helpButton = new UIButton();
//....
// code to create our custom button with background
// .....
UIBarButtonItem helpBarButton = new UIBarButtonItem(_helpButton);
items.Add(helpBarButton);
When showing our VC, we show the toolbar and everything looks great. On
the VC, we have a button that opens another VC(as the root view of another
UINavigationController) as a modal FormSheet. In ViewDidAppear, we also
set the toolbar to visible, which would show the same help button, which
also works great.
Once the modal VC is shown, since it's not full screen, you can still see
the other VC in the background. The toolbar on the background VC no longer
has the help button visible(the Toolbar is still showing). There is no
code that removes or hides the help button, so I'm not sure what is
happening to it.
As I don't really know how to set this scenario up in objective-c, I'm not
sure if this is an iOS issue, a Xamarin.iOS issue, or an issue with my
understanding of the toolbar.