Doesn't save user settings, or rather, once unchecked always unchecked

I can't enable them. Checking them and clicking save doesn't save my changes.

Ok, weird, because it keeps happening.

My tables schemas are below. I've attached my copy of the module.

-- 
-- Table structure for table `privatemsg`
-- 

CREATE TABLE `privatemsg` (
  `id` int(10) unsigned NOT NULL auto_increment,
  `author` int(10) unsigned NOT NULL default '0',
  `recipient` int(10) unsigned NOT NULL default '0',
  `subject` varchar(64) NOT NULL default '',
  `message` text,
  `timestamp` int(11) unsigned NOT NULL default '0',
  `newmsg` tinyint(3) unsigned NOT NULL default '0',
  `hostname` varchar(255) NOT NULL default '',
  `folder` int(10) unsigned NOT NULL default '0',
  `author_del` tinyint(3) unsigned NOT NULL default '0',
  `recipient_del` tinyint(3) unsigned NOT NULL default '0',
  `format` int(4) NOT NULL default '0',
  PRIMARY KEY  (`id`),
  KEY `recipient` (`recipient`),
  KEY `folder` (`folder`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;


-- 
-- Table structure for table `privatemsg_archive`
-- 

CREATE TABLE `privatemsg_archive` (
  `id` int(10) unsigned NOT NULL auto_increment,
  `author` int(10) unsigned NOT NULL default '0',
  `recipient` int(10) unsigned NOT NULL default '0',
  `subject` varchar(64) NOT NULL default '',
  `message` text NOT NULL,
  `timestamp` int(11) unsigned NOT NULL default '0',
  `hostname` varchar(255) NOT NULL default '',
  `folder` int(10) unsigned NOT NULL default '0',
  `format` int(4) NOT NULL default '0',
  PRIMARY KEY  (`id`),
  KEY `recipient` (`recipient`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;



-- 
-- Table structure for table `privatemsg_folder`
-- 

CREATE TABLE `privatemsg_folder` (
  `fid` int(10) unsigned NOT NULL auto_increment,
  `uid` int(10) unsigned NOT NULL default '0',
  `name` varchar(255) NOT NULL default '',
  PRIMARY KEY  (`fid`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ;

The boxes are checked by default but if you uncheck them and click SUBMIT, they will get and remain unchecked. However if you go back to the Edit tab, check them and click SUBMIT, when you view the Edit tab again they remain empty and unchecked. Any clues?