Android : Avoid Android APK to run multiple instances

In our AndroidManifest.xml, we added android:launchMode="singleInstance" to avoid multiple instances running at the same time.

However, the App now runs in 2 instances at the same time.

This issue only appears when we installed via APK using signed production keystore; when we run in Eclipse, the same issue does not happen at all.

Where else I overlooked ?

p.s. we tried singleTop and singleTask too.