While developing an Android app targeting all versions above 4.1, I observed that uninstalling my app and installing it again does not clear its data.
The app is designed to store the details that it asks in its first screen. After uninstalling and installing again in OS version 4.4.4, the app prompts the user to fill in the data, which is normal. However in version 6.0 the same install/uninstall sequence bring backs the data originally input.
I tried to ensure by visiting /data/data/my package folder to see the database is gone after uninstalling and indeed that folder gets deleted during uninstall.
I tried to delete the app by visiting the settings page, through Titanium Backup and the results are same. The device is rooted Nexus 5 running v6.0.
What could be the reason for this strange behavior?
It's because Android 6 has automatic backup. You need to tune android:allowBackup and android:fullBackupContent in your manifest <application> tag if you don't want your data backed up or if you want to include or exclude some resources. It's not a bug.
More about AutoBackup on Android here.