Button with getBackground().setAlpha on version 5 - lollipop isn't working correctly

Question

I have this code and works for every version since API 14 but on Android 5.0 (Lollipop) isn't working correctly.

Below is the way how I want the buttons to appear.

click of button1

buttonArrivals.getBackground().setAlpha(180);
buttonDepartures.getBackground().setAlpha(255);

click of button2

buttonArrivals.getBackground().setAlpha(255);
buttonDepartures.getBackground().setAlpha(180);

On the Lollipop version, the buttons appear with the same Alpha but I never set the same alpha. I just use the code above.

UPDATE 24/11/2014

Here is the XML of the buttons (AutoResizeButton extends Button)

br.com.timo.gru.util.AutoResizeButton
            android:id="@+id/buttonArrivals"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="2"
            android:background="#00abbd"
            android:drawableLeft="@drawable/icon_aviao_desemb"
            android:drawablePadding="-5dp"
            android:drawableStart="@drawable/icon_aviao_desemb"
            android:gravity="center"
            android:paddingEnd="0dp"
            android:paddingLeft="2dp"
            android:paddingRight="0dp"
            android:text="@string/chegadas"
            android:textColor="@android:color/white"

br.com.timo.gru.util.AutoResizeButton
            android:id="@+id/buttonPartidas"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="2"
            android:background="#00abbd"
            android:drawableLeft="@drawable/icon_aviao_partida"
            android:drawablePadding="-5dp"
            android:drawableStart="@drawable/icon_aviao_partida"
            android:ellipsize="end"
            android:gravity="center"
            android:text="@string/partidas"
            android:textColor="@android:color/white"

Answer 1

Internally ColorState (used by ColorDrawable) is shared between these 2 buttons (optimization), so whenever you change alpha on one button's background - other button will get this change as well. You can try to to mutate background drawable before changing its alpha:

buttonArrivals.getBackground().mutate().setAlpha(180);
buttonDepartures.getBackground().mutate().setAlpha(255);

You can also read good explanation from Romain Guy on why this is happening: http://curious-creature.org/2009/05/02/drawable-mutations

However, it looks like you try to implement something which is easily achievable with Android selectors. You can specify different color for each button state (in your case selected/not selected), so in your code you just need to update state:

buttonArrivals.setSelected(true);
buttonDepartures.setSelected(false);

And selector would look like:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:color="#ff00abbd"
        android:state_selected="true" >
    </item>

    <item android:color="#b400abbd"
        android:state_selected="false">
    </item>

</selector>