Orchard - save list of elements on form submit

Question

Basically i have a editor view where i have a few fields and a list, located in admin -> teacher -> edit

File.cshtml

<fieldset>
    <legend>@T("Details")</legend>
    @Html.LabelFor(m => m.FirstName, T("First name"))
    @Html.TextBoxFor(m => m.FirstName)
    @Html.LabelFor(m => m.LastName, T("Last name"))
    @Html.TextBoxFor(m => m.LastName)
    @Html.LabelFor(m => m.Gender, T("Gender"))
    @Html.DropDownListFor(m => m.Gender, genderSelectListItems, "Select gender...")
</fieldset>

<fieldset>
@{
    var i = 0;
    @Html.LabelFor(m => m.Availability)
    @Html.DropDownListFor(m => m.Availability, daysSelectList, "Select day to add...")
    <input type="button" id="addDay" value="Add" />
    <ul id="daysList">
        @foreach (var day in Model.Availability)
        {
            <li>
                @Html.TextBoxFor(m => m.Availability[i].Interval)
            </li>
            i++;
        }
    </ul>
}
</fieldset>

Whenever i submit the data, only the fields get saved. The list is never saved, even though fiddler shows that the data is sent back to the server

My models are:
TeacherPartRecord

public class TeacherPartRecord : ContentPartRecord
{
    public TeacherPartRecord()
    {
        TeacherData = new List<TeacherDataRecord>();
    }

    public virtual string FirstName { get; set; }
    public virtual string LastName { get; set; }
    public virtual Gender Gender { get; set; }

    public virtual IList<TeacherDataRecord> TeacherData { get; set; }
}

TeacherPart - this file is almost the same as TeacherPartRecord so i truncated it, showing only the difference

public class TeacherPart : ContentPart<TeacherPartRecord>
{
      ................  
    public IList<AvailabilityRecord> Availability
    {
        get { return Record.TeacherData.Select(r => r.AvailabilityRecord).ToList(); }
    }
}

TeacherDataRecord

public class TeacherDataRecord
{
    public virtual int Id { get; set; }
    public virtual TeacherPartRecord TeacherPartRecord { get; set; }
    public virtual AvailabilityRecord AvailabilityRecord { get; set; }
}

AvailabilityRecord

public class AvailabilityRecord
{
    public virtual int Id { get; set; }
    public virtual Day Day { get; set; }
    public virtual string Interval { get; set; }
}

and TeacherPartDriver

public class TeacherPartDriver : ContentPartDriver<TeacherPart>
{
    //GET
    protected override DriverResult Editor(TeacherPart part, dynamic shapeHelper)
    {
        return ContentShape("Parts_Teacher_Edit", () => 
            shapeHelper.EditorTemplate(TemplateName: "Parts/Teacher", Model: BuildEditorViewModel(part), Prefix: Prefix));
    }

    //POST
    protected override DriverResult Editor(TeacherPart part, IUpdateModel updater, dynamic shapeHelper)
    {
        var viewModel = new TeacherEditViewModel();
        updater.TryUpdateModel(viewModel, Prefix, null, null);
        _teacherService.UpdateTeacher(viewModel, part);
        return Editor(part, shapeHelper);
    }
}

BuildEditorViewModel only maps properties from TeacherPart to TeacherEditViewModel, which is identical with TeacherPart

The POST Editor method never receives the data from Availability (part.Availability is the same as previously, new data is not received)

I inserted a few entries in the database manually because i can't add a list of type Availability from the edit page, even though the other content (first name, last name, gender) is created

I would like to know how/when does the binding occur, or maybe some suggestions on how i could solve this issue.

I should mention that my c#/MVC experience is 6 months and my orchard experience is about 2 weeks so i'm still learning. All i hope is that i stated my problem clearly and there is someone that can help. Thank you for your time

EDIT As i can see, the values are bound

<input id="Teacher_Availability_0__Interval" name="Teacher.Availability[0].Interval" type="text" value="14-20">
<input id="Teacher_Availability_1__Interval" name="Teacher.Availability[1].Interval" type="text" value="12-18">

and fiddler shows the data is getting sent

Fiddler

so i guess that something wrong happens right after the data is sent and before being received by the server or maybe my models are wrong