SelectDateWidget generate an HTML-error (reference to non-existent ID "id_birthday")
This is the rendered HTML code:
<tr><th><label for="id_birthday">Birthday:</label></th><td><select name="birthday_month">
<option value="1">Januar</option>
<option value="2">Februar</option>
<option value="3">März</option>
<option value="4">April</option>
<option value="5">Mai</option>
<option value="6">Juni</option>
<option value="7">Juli</option>
<option value="8">August</option>
<option value="9">September</option>
<option value="10">Oktober</option>
<option value="11">November</option>
<option value="12">Dezember</option>
</select>
<select name="birthday_day">
<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="birthday_year">
<option value="1950">1950</option>
.....
<option value="1991">1991</option>
</select></td></tr>
