<form action="{{ action }}" method="post" id="form" class="form-assign-mentor">
  <div id="form_fields_assign_mentor">
    <select name="assign_mentor" id="id_assign_mentor">
      <option value="">Assign a mentor</option>
      {% if possible_mentors %}
        <optgroup label="Possible Mentors">
          {% for m in possible_mentors %}
            <option value="{{ m.key }}" {% if m.selected %}selected="selected"{% endif %}>{{ m.name }}</option>
          {% endfor %}
        </optgroup>
      {% endif %}
      {% if all_mentors %}
        <optgroup label="All Mentors">
          {% for m in all_mentors %}
            <option value="{{ m.key }}" {% if m.selected %}selected="selected"{% endif %}>{{ m.name }}</option>
          {% endfor %}
        </optgroup>
      {% endif %}
    </select>
    <input id="form-project-assign-mentor-submit" type="submit" value="Assign"/>
    <span class="note">Select a mentor from the drop-down list to assign to this proposal. <br/>
    {% if not all_mentors %}
      Note that only mentors that have clicked the "I wish to mentor this project" button can be selected.</span>
    {% endif %}
  </div>
</form>

<form action="{{ action }}" method="post" id="form" class="form-assign-mentor">
  <div id="form_fields_assign_mentor">
    <select name="assign_mentor" id="id_assign_mentor">
      <option value="">Assign a mentor</option>
      {% if possible_mentors %}
        <optgroup label="Possible Mentors">
          {% for m in possible_mentors %}
            <option value="{{ m.key }}" {% if m.selected %}selected="selected"{% endif %}>{{ m.name }}</option>
          {% endfor %}
        </optgroup>
      {% endif %}
      {% if all_mentors %}
        <optgroup label="All Mentors">
          {% for m in all_mentors %}
            <option value="{{ m.key }}" {% if m.selected %}selected="selected"{% endif %}>{{ m.name }}</option>
          {% endfor %}
        </optgroup>
      {% endif %}
    </select>
    <input id="form-project-assign-mentor-submit" type="submit" value="Assign"/>
    <span class="note">Select a mentor from the drop-down list to assign to this proposal. <br/>
    {% if not all_mentors %}
      Note that only mentors that have clicked the "I wish to mentor this project" button can be selected. <br/>
      This can be changed in the organization profile page under "Organization preferences".
    {% endif %}
    </span>
  </div>
</form>

Move /span outside endif, add note about org preferences
Move /span outside endif, add note about org preferences
