Back button does not change text dynamically

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


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

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