I'm getting a strange behaviour from form_dropdown - basically, when I reload the page after validation, the values are screwed up.

this bit generates 3 drop downs with days, months and years:

$days = array(0 => 'Day...');
        for ($i = 1; $i <= 31; $i++)
        {
            $days[] = $i;
        }
        $months = array(0 => 'Month...', );
        for ($i = 1; $i <= 12; $i++)
        {
            $months[] = $i;
        }
        $years = array(0 => 'Year...');
        for ($i = 2010; $i <= 2012; $i++)
        {
            $years[$i] = $i; 
            echo "<pre>"; print_r($years); echo "</pre>";//remove this
        }

        $selected_day = (isset($selected_day)) ? $selected_day : 0;
        $selected_month = (isset($selected_month)) ? $selected_month : 0;
        $selected_year = (isset($selected_year)) ? $selected_year : 0;
        echo "<p>";
            echo form_label('Select date:', 'day', array('class' => 'left'));
            echo form_dropdown('day', $days, $selected_day, 'class="combosmall"'); 
            echo form_dropdown('month', $months, $selected_month, 'class="combosmall"'); 
            echo form_dropdown('year', $years, $selected_year, 'class="combosmall"'); 
        echo "</p>";

...and generates this:

    <p><label for="day" class="left">Select date:</label><select name="day" class="combosmall"> 
<option value="0" selected="selected">Day...</option> 
<option value="1">1</option> 
<option value="2">2</option> 
<option value="3">3</option> 
<option value="4">4</option> 
<option value="5">5</option> 
<option value="6">6</option> 
<option value="7">7</option> 
<option value="8">8</option> 
<option value="9">9</option> 
<option value="10">10</option> 
<option value="11">11</option> 
<option value="12">12</option> 
<option value="13">13</option> 
<option value="14">14</option> 
<option value="15">15</option> 
<option value="16">16</option> 
<option value="17">17</option> 
<option value="18">18</option> 
<option value="19">19</option> 
<option value="20">20</option> 
<option value="21">21</option> 
<option value="22">22</option> 
<option value="23">23</option> 
<option value="24">24</option> 
<option value="25">25</option> 
<option value="26">26</option> 
<option value="27">27</option> 
<option value="28">28</option> 
<option value="29">29</option> 
<option value="30">30</option> 
<option value="31">31</option> 
</select><select name="month" class="combosmall"> 
<option value="0" selected="selected">Month...</option> 
<option value="1">1</option> 
<option value="2">2</option> 
<option value="3">3</option> 
<option value="4">4</option> 
<option value="5">5</option> 
<option value="6">6</option> 
<option value="7">7</option> 
<option value="8">8</option> 
<option value="9">9</option> 
<option value="10">10</option> 
<option value="11">11</option> 
<option value="12">12</option> 
</select><select name="year" class="combosmall"> 
<option value="0" selected="selected">Year...</option> 
<option value="2010">2010</option> 
<option value="2011">2011</option> 
<option value="2012">2012</option> 
</select></p>

however, when the form is reloaded after validation, the same code above generates this:

<!-- days and months... -->
<select name="year" class="combosmall"> 
<option value="0" selected="selected">Year...</option> 
<option value="1">2010</option> 
<option value="2">2011</option> 
<option value="3">2012</option> 
</select>

So basically the value start from 1 instead of 2010. The same happens to days and months but obviously it doesn't make any difference in this particular case as the values would start from 1 anyway.

How can I fix this - and why does it happen?

edit: validation rules are:

$this->load->library('form_validation');
//...rules for other fields..
$this->form_validation->set_rules('day', 'day', 'required|xss_clean');
$this->form_validation->set_rules('month', 'month', 'required|xss_clean');
$this->form_validation->set_rules('year', 'year', 'required|xss_clean');        
$this->form_validation->set_error_delimiters('<p class="error">', '</p>');
//define other errors
if($this->input->post('day') == 0 || $this->input->post('month') == 0 || $this->input->post('year') == 0) 
    {
        $data['error'] = "Please check the date of your event.";
    }