Error on using proguard with Android Facebook sdk 3.0

Warning: I removed a lot of "old text" to keep the question more clean. Just check the history if needed.

I'm using proguard to both shrink and obfuscate an app that uses the facebook sdk 3.0 (I'm using the sdk-version-3.0.2.b tag). I'm not using a JAR file. Instead, I imported the sdk inside my workspace, as taught by the documentation.

At a certain point in the execution, the app loads a PlacePickerFragment to let the user choose the place where he is. To code this, I follow exactly the Scrumptious tutorial. When I generate the debug apk without using proguard everything works as expected. But when I generate the signed apk using proguard, it crashes when the PlacePickerFragment loads nearby places with the following trace:

E/AndroidRuntime(27472): FATAL EXCEPTION: main
E/AndroidRuntime(27472): com.facebook.FacebookGraphObjectException: can't infer generic type of: interface com.facebook.model.GraphObjectList
E/AndroidRuntime(27472):    at com.facebook.model.GraphObject$Factory.coerceValueToExpectedType(Unknown Source)
E/AndroidRuntime(27472):    at com.facebook.model.GraphObject$Factory$GraphObjectProxy.proxyGraphObjectGettersAndSetters(Unknown Source)
E/AndroidRuntime(27472):    at com.facebook.model.GraphObject$Factory$GraphObjectProxy.invoke(Unknown Source)
E/AndroidRuntime(27472):    at com.facebook.widget.$Proxy2.getData(Native Method)