Floating Action Button does not responds when it clicked/touched

Question

I am using a floating action button(FAB) in my application to show Dialogs, everything is worked just fine when I tested my app in Xperia Z with Lopllipop 5.1.1.
However

Answer 1

Programmatically bringing the FAB to front should also work:

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.bringToFront();
fab.setOnClickListener... //etc