TabPage Title change throws NullPointerException

I am facing issues with TabPage when I try to append some data in title. Scenario as below ..

1. From Search page -> Tabbed Page to display details . 2nd tab page, which has a list is updated asynchronously. Once received list updated event, populate list and update tab page Title ( In this scenario everything works)
2. From Tabbed Page -> Update page. Here user can update and go back to Tab page. Once again based on updated data, list is updated and tab page Title should reflect new item count. But here I get a NullPointerException.
   I saw a bug reported in xamarin.Forms but marked as not reproduce able. (https://bugzilla.xamarin.com/show_bug.cgi?id=27350)

Any idea how to trace this issue?