Как настроить ProGuard для Amazon IAP?

Я пытаюсь установить базовый ProGuard с интегрированным Amazon IAP. Однако, когда я пытаюсь экспортировать свой APK, я получаю следующие ошибки:

[2012-06-17 10:59:44 - sc] Proguard returned with error code 1. See console
[2012-06-17 10:59:44 - sc] Unexpected error while performing partial evaluation:
[2012-06-17 10:59:44 - sc]   Class       = [com/amazon/inapp/purchasing/KiwiResponseHandler$PurchaseResponseHandlerRunnable]
[2012-06-17 10:59:44 - sc]   Method      = [run()V]
[2012-06-17 10:59:44 - sc]   Exception   = [java.lang.IllegalArgumentException] (Can't find common super class of [java/lang/String] (with 4 known super classes) and [com/amazon/inapp/purchasing/KiwiPurchaseResponseCommandTask] (with 1 known super classes))
[2012-06-17 10:59:44 - sc] java.lang.IllegalArgumentException: Can't find common super class of [java/lang/String] (with 4 known super classes) and [com/amazon/inapp/purchasing/KiwiPurchaseResponseCommandTask] (with 1 known super classes)
[2012-06-17 10:59:44 - sc]  at proguard.evaluation.value.ReferenceValue.generalize(ReferenceValue.java:344)
[2012-06-17 10:59:44 - sc]  at proguard.evaluation.value.IdentifiedReferenceValue.generalize(IdentifiedReferenceValue.java:65)
[2012-06-17 10:59:44 - sc]  at proguard.evaluation.value.ReferenceValue.generalize(ReferenceValue.java:481)
...

У меня есть файл конфигурации ProGuard по умолчанию, и я уже добавил в него строки:

 -dontwarn com.amazon.**
 -keep class com.amazon.** {*;}
 -keepattributes *Annotation*

. Есть предположения, что пошло не так?