Back button does not change text dynamically

Ionic Framework ionic-v3
1

After setting back button text using config,
it does not reflect right away in nav bar.
Have to pop and push the page again.

playground:


you can see in contact page,
setting back button text does not reflect in self page and even in other nav stack

I suspect this is a bug and have opened a issue:


and find another issue similar:

is that a ionic bug / my program bug?
hope to see advice

2

One workaround is to set view controller’s back button text every time entered the page