core_user_create_users causes "active database transaction detected during request shutdown" errors

Hi,

Not entirely sure what the story with this is. The function works fine and there's no problems at all except every time I use it I get this lovely error filling up Apache's error logs...

[Mon Jul 07 11:39:58 2014] [error] [client 193.169.192.110] Potential coding error - active database transaction detected during request shutdown:\n
• line 122 of /user/externallib.php: call to moodle_database->start_delegated_transaction()\n
• line 17 of /webservice/lib.php(1275) : eval()'d code: call to core_user_external::create_users()\n
• line ? of unknownfile: call to webservices_virtual_class_000000->core_user_create_users()\n* 
• line 232 of /lib/zend/Zend/Server/Abstract.php: call to call_user_func_array()\n* 
• line 599 of /lib/zend/Zend/XmlRpc/Server.php: call to Zend_Server_Abstract->_dispatch()\n* 
• line 337 of /lib/zend/Zend/XmlRpc/Server.php: call to Zend_XmlRpc_Server->_handle()\n* 
• line 1179 of /webservice/lib.php: call to Zend_XmlRpc_Server->handle()\n* 
• line 55 of /webservice/xmlrpc/server.php: call to webservice_zend_server->run()\n

What I can't decide on is - what could be causing this?

If it's creating users just fine with the information it gets. Is there a problem with the webservice itself or the way it's being touched?

Anyone with any thoughts?