unobtrusive validation not firing on nullable date field - asp.net-mvc-3

Question

I have an Edit View, with a select list and a couple text boxes that are generated for nullable date fields. When there is no date present, no validation occurs - this is correct.
However, if I input an invalid date, the validation does not detect that, and proceeds to my action. How can I force validation on the date fields?
My model:
public class CaseEmployer
{
public int Id { get; set; }
public int CaseId { get; set; }
public Company Company { get; set; }
[Display(Name = "Start Date")]
[DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}", ApplyFormatInEditMode=true)]
public DateTime? StartDate { get; set; }
[Display(Name = "End Date")]
[DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}", ApplyFormatInEditMode = true)]
public DateTime? EndDate { get; set; }
public int? UserId { get; set; }
public DateTime? TimeStamp { get; set; }
}
My View:
#using (Html.BeginForm())
{
#Html.ValidationSummary(true)
<fieldset>
<legend>Employer</legend>
#Html.HiddenFor(model => model.Id)
#Html.HiddenFor(model => model.CaseId)
<div class="editor-label">
#Html.Label("Company:")
</div>
<div class="editor-field">
<select name="companySelect" id="companySelect">
#foreach (var company in ViewBag.CompanyOptions)
{
<option value="#company.Key">#company.Value</option>
}
</select>
</div>
<div class="editor-label">
#Html.LabelFor(model => model.StartDate)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.StartDate)
#Html.ValidationMessageFor(model => model.StartDate)
</div>
<div class="editor-label">
#Html.LabelFor(model => model.EndDate)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.EndDate)
#Html.ValidationMessageFor(model => model.EndDate)
</div>
<p>
<input type="submit" value="Update" />
<input type="button" value="Cancel" onclick="javascript:window.close()" />
<input type="button" value="Delete" onclick="javascript:confirmDeleteCaseEmployer()" />
</p>
</fieldset>
** Edit **
I added "Required" attributes to the class to test if the validation would trigger, if I submitted the form without StartDate and EndDate, and the validation does trigger with those attributes.
Thank you!

Answer 1

If you intend on having the date time fields validated, you'll probably want to look into a regularexpression validate attribute to help the client side unobtrusive JavaScript to validate the expected input. Your displayformat attributes won't affect validation, only the way the datetime value is displayed.
With your code as displayed, there's basically no validation happening until the form posts to the controller action. Since updatemodel is unable to convert some of your input into a datetime value, you're getting model format conversion errors.