Okay, got it working by making sure, that the Proguard generated files are always cleared before assembling. This is necessary as the -forceprocessing
flag supplied by the Proguard Gradle plugin unfortunately didn't have any effect.
android.buildTypes.all{ buildType ->
task "${buildType.name}CleanProguardCache" (type: Delete)
"${buildType.name}CleanProguardCache" {
description = 'Cleans the Proguard cache...'
delete 'build/classes-proguard', 'build/proguard'
}
tasks.getByPath(":${project.name}:assemble${buildType.name.capitalize()}").dependsOn "${buildType.name}CleanProguardCache"
}
The clean task is applied to all build types like explained here.
EDIT: As Xavier Ducrohet points out here there seems to be a bug in the Proguard task setup which causes the described problem. The fix will be part of the next Android Gradle Plugin version.
EDIT 2: As promised this bug is fixed in the Android Gradle Plugin 0.10.0. Therefore the workaround is obsolete for this plugin version.