SQLite Connection leaked although everything closed

The bolded font in the citation corresponds to this part in your code:

private DatabaseManager open() throws SQLException {
    dbHelper = new DatabaseHelper(context);
    db = dbHelper.getWritableDatabase();

from: http://www.androiddesignpatterns.com/2012/05/correctly-managing-your-sqlite-database.html

Approach #1: Use an Abstract Factory to Instantiate the
SQLiteOpenHelper

Declare your database helper as a static instance variable and use the
Abstract Factory pattern to guarantee the singleton property. The
sample code below should give you a good idea on how to go about
designing the DatabaseHelper class correctly.

The static factory getInstance method ensures that only one
DatabaseHelper will ever exist at any given time. If the mInstance
object has not been initialized, one will be created. If one has
already been created then it will simply be returned.

You should
not initialize your helper object using with new DatabaseHelper(context).
Instead, always use
DatabaseHelper.getInstance(context), as it guarantees that only one
database helper will exist across the entire application’s lifecycle.

public static class DatabaseHelper extends SQLiteOpenHelper { 

  private static DatabaseHelper mInstance = null;

  private static final String DATABASE_NAME = "database_name";
  private static final String DATABASE_TABLE = "table_name";
  private static final int DATABASE_VERSION = 1;

  public static DatabaseHelper getInstance(Context ctx) {

    // Use the application context, which will ensure that you 
    // don't accidentally leak an Activity's context.
    // See this article for more information: http://bit.ly/6LRzfx
    if (mInstance == null) {
      mInstance = new DatabaseHelper(ctx.getApplicationContext());
    }
    return mInstance;
  }

  /**
   * Constructor should be private to prevent direct instantiation.
   * make call to static factory method "getInstance()" instead.
   */
  private DatabaseHelper(Context ctx) {
    super(ctx, DATABASE_NAME, null, DATABASE_VERSION);
  }
}