When searching there is a flood control in place, However this is globalized via $config and will effect other users overall.

Search.php

// Check last search time ... if applicable

if ($config['search_interval'])

{

	if ($config['last_search_time'] > time() - $config['search_interval'])

	{

		trigger_error($user->lang['NO_SEARCH_TIME']);

	}

}

This needs to be session based like the fix that was applied to phpBB 2.0.X CVS (.20)