Can not find Driver when using generic database bundle

I have a project that is build up from several OSGi bundles. One of them is a generic Database bundle that defines a DataSource that can be used throughout the project. The spring bean definition of this service is:

<osgi:service interface="javax.sql.DataSource">
    <bean class="org.postgresql.ds.PGPoolingDataSource">
        <property name="databaseName" value="xxx" />
        <property name="serverName" value="xxx" />
        <property name="user" value="xxx" />
        <property name="password" value="xxx" />
    </bean>
</osgi:service>

Now, when using this DataSource is a different bundle, we get an error:

No suitable driver found for jdbc:postgresql://localhost/xxx

I have tried the following to add the org.postgresql.Driver to the DriverManager:

1. Instantiated an empty bean for that Driver in the spring context, like this:
   <bean class="org.postgresql.Driver" />

2. Instantiated the Driver statically in one of the classes, like this:
   Class.forName("org.postgresql.Driver");

   a. Also tried this while adding the org.postgresql package as DynamicImport-Package.

3. Added a file META-INF\services\java.sql.Driver with the content org.postgresql.Driver

None of these solutions seems to help.

I've found the solution, or at least a workaround. In my abstract DAO I've added the following:

static {
  try {
    DriverManager.registerDriver(new org.postgresql.Driver());
  } catch(SQLException ex) {
    LogFactory.getLogger(AbstractDAO.class).error("Could not load Driver", ex);
  }
}

This does seem to work. Does anyone know why? It is not that different from the Class.forName solution.