Getting InvalidClassException in a BroadcastReceiver after enabling obfuscating on my project

Question

My project works fine, but as soon as I start obfuscating the code I get the following exception

Fatal Exception: java.lang.RuntimeException: Parcelable encountered IOException reading a Serializable object (name = com.mypackage.service.b.a) Caused by java.io.InvalidClassException: com.mypackage.service.b.a); class invalid for deserialization

This is happening in the following BroadcastReceiver

    public class MyReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(final Context context, Intent intent) {
        if (intent != null) {
            UpdateServiceConfig config = null;
            final Bundle bundle = intent.getBundleExtra(Keys.DATA);
            if (bundle != null) {
crash   =>          config = (UpdateServiceConfig) bundle.getSerializable(Keys.CONFIG);
            }
        }
    }
}

Here are my Proguard rules

-keepnames class * implements java.io.Serializable

-keepclassmembers class * implements java.io.Serializable {
    static final long serialVersionUID;
    private static final java.io.ObjectStreamField[] serialPersistentFields;
    !static !transient <fields>;
    !private <fields>;
    !private <methods>;
    private void writeObject(java.io.ObjectOutputStream);
    private void readObject(java.io.ObjectInputStream);
    java.lang.Object writeReplace();
    java.lang.Object readResolve();
}

-keep class com.mypackage.service.config.UpdateServiceConfig { *; }
-keep class com.mypackage.service.config.config.** { *; }

There are other parts of the app where this class is retrieved from a bundle in the exact same way without any excpetion. It looks like the fact that this is handled in a BroadcastReceiver is what's causing the issue. Any idea what's causing this and how to fix that?