I did some research with these results:
I have 4 tabs in my application and multiple views in each tab. The error appears when I navigate to the tab 1 (no back button since I’m on its first view), then I navigate to the tab 2 and to the another view within this tab. Back button appears for the tab 2.
Then I navigate to the tab 1. The placeholder for back button is displayed even though tab 1 has no navigation history - it probably “inherits” the history from the tab 2 which I came from.
When I navigate to the tab 2 again, the back button is overlapping the title of the tab 2 - back button is (and should be) there since I lend on the second view within the tab 2 but for the title the information about the button is probably missing so the title has no left margin and overlaps the back button.
The overlapping problem also occurs, when you navigate from Page 1 to Page 2 and both have the same title. After changing the title it works.