Cracked it. In case anyone needs this, the android:allowBackup="false" is set as default in platform/android/java/AndroidManifest.xml. This needs to be set as "true".
Unfortunately, if you are not using any custom package, you cannot change this option to reflect directly in your game. In that case, you can maybe, create a dummy package, , and then change the AndroidManifest.xml file. The resulting custom apk generated can then be specified in the export options and engine.cfg.
That's would be totally unnecessary though. Maybe, the creators can export this as an option in the UI editor??