How can I active my listbox?

I meet a big problem.  I defines an listbox and a button,then add keyboard listener with "Up" and "Down" to listbox .The problem is that,when I enter the ↑ or ↓,the UI automatically set the button active,not the listbox!

I used listbox.active = true in eventListener.But,it only works for the first time . After that ,every time I enter the keys,the UI still set other button active! To my supprise,the value of the button.active is false while the listbox.active is true!!!!!  I don't know what happens.Maybe something wrong happens after my eventListener?

My ae is ae cc 2014.2.However,in ESTK  there is not the problem.

Any help can be very appreciated!