ちっ、なんなんだよこれは。
デバッグ版はエミュレータでも実機でも問題なく処理できますが。
Issue 60762 - android - Problem wen generate apk - Android Open Source Project - Issue Tracker - Google Project Hosting
ちっ。
対応方法を探します。
In the latest version of Android Studio (0.2.11) Generate Signed Apk no longer works. You're directed to set up a signing configuration in your gradle.bundle file, which (presumably) has to be run by hand from the command line unless you're willing to hardcode your password there
How to set up gradle and android studio to do release build? - Stack Overflow 
I ended up just using "gradle installRelease" and coping the release APK from build/apk folder.
I am not sure why we are getting this, I do have my signingConfigs setup properly in build.gradle.
Android Studio: Signing issue after upgrade - Stack Overflow 
android {
signingConfigs {
debug {
storeFile file("debug.keystore")
}
myConfig {
storeFile file("other.keystore")
storePassword "android"
keyAlias "androiddebugkey"
keyPassword "android"
}
}
buildTypes {
foo {
debuggable true
jniDebugBuild true
signingConfig signingConfigs.myConfig
}
}
}
Gradle Plugin User Guide - Android Tools Project Site 
build.gradle を上記を参考に記述して、
$ gradle installRelease
と実行して、build/apk フォルダ内にapkを取ってきましたけど。
build.gradle にパスワードとかプレーンで書くとかどうなのか、
AndroidStudio のパスワード管理まわりが未対応なのかな。
（※ 再起動したらいけるときもあったりしたよ。）
