Trouble with auto including generate Base class with specifik name

I have found a problem during testing example model on page http://www.doctrine-project.org/documentation/cookbook/1_1/en/code-igniter-and-doctrine . A use YAML model with object name UserGroup and call method Doctrine_Core::createTablesFromModels('models'); process faling with error:

Fatal error: Class 'BaseUserGroup' not found in /sourcepath/models/UserGroup.php on line 13

Generate model file included abstract class BaseUserGroup exist and is OK. If I include BaseUserGroup manuly or rename object "UserGroup" on "UserGroups" everithing work fine. I thing here is a problem with autoloding base class with specifik name.

Here is my code example:

Doctrine_Core::dropDatabases();
Doctrine_Core::createDatabases();
Doctrine_Core::generateModelsFromYaml('sourcepath/yaml/model.yml', 'models');
Doctrine_Core::createTablesFromModels('models');

Trouble shotting YAML model is:
—
UserGroup:
columns:
user_id:
type: integer(4)
primary: true
group_id:
type: integer(4)
primary: true