I see some unexplained Proguard behaviour.
AFAIK proguard does not pay attention to android manifest. Also, in my proguard.cfg I have no mention of BroadcastReceiver
The build process runs the tool aapt to automatically create the configuration file bin/proguard.txt, based on AndroidManifest.xml and other xml files. The build process then passes the configuration file to ProGuard. So ProGuard itself indeed doesn't consider AndroidManifest.xml, but aapt+ProGuard do.