4.6 uGUI Mobile - Touch Button not working.

I have this issue where on an Android device buttons seems to fail to call the event handler.
I can see how the button sprites changes indicating that the button was pressed but the event is not called.
This seems to happen randomly, it can work fine and sometimes you need to repeat a few touches 4-5 to get the event fired.

There is a similar thread here but it does not seems to have been fixed yet.
So I have two questions:

1. Is this bug fixed or in the works?
2. How can I address this issue to make sure that every time the player touches the button the event is fired?

regards