Rather than guessing why not just fire up Fiddler (or similar) and see what's actually going over the wire. If you are getting padding then debug in the browser.....

>>>Now it seems to be 'String or Binary data will be truncated message'. Strange again as I only put few characters in the Address field and didn't change anything else. Luckily I think I'll be able to figure out this problem using profiler.
>>
>>Are you sure that nothing on the browser is padding that value ?
>
>No, not sure at all. I am going to go deeper now into this - how the browser would pad data? Also, do you have an idea why my StringLength(5) condition was breaking for Ext while I didn't even touch it?
>
>Could it be in the way I have my view defined and the Editor Templates?
>
>The view is
>

>@using CardNumbers.Helper
>@model CardNumbers.Models.ClientViewModel
>  <form id="add-edit-form">
>    <fieldset>
>        <legend>Client Info</legend>
>
>        @Html.ValidationSummary(true)
>       
>        <input type="hidden" id="fntype" name="fntype" value="Edit">
>
>        @Html.HiddenFor(m => m.ClientId)
>        @Html.EditorFor(m => m.ClientNumber, EditorTemplate.TextBox)
>
>        @Html.EditorFor(m => m.ClientName, EditorTemplate.TextBox)
>
>        @Html.EditorFor(m => m.Client.Address, EditorTemplate.EditBox)
>
>        <div id="ContactsInfo">
>
>            <div id="Contact1">
>
>                @Html.EditorFor(m => m.Client.Contact1)
>
>            </div>
>
>            <div id="Contact2">
>
>                @Html.EditorFor(m => m.Client.Contact2)
>            </div>
>        </div>
>
>       @* <div id="SaveCancel" class="float-right">
>            <button id="btnSave">Save</button>
>            <button type="reset" id ="btnCancel" name="Reset">Cancel</button>
>        </div>*@
>    </fieldset>
>
> </form>

>
>I think it's simple enough.
>
>The Editor Templates:
>
>TextBox template
>
>

><div class="editor-label">
>    @Html.Label((ViewData.ModelMetadata.DisplayName??ViewData.ModelMetadata.PropertyName),
>        new Dictionary<string, object>
>            {                
>                { "for", ViewData.ModelMetadata.PropertyName }
>            })
></div>
>
><div class="editor-field">
>   @if (ViewData.ModelMetadata.ModelType.IsNumeric())
>   {
>    @Html.TextBox("", ViewData.TemplateInfo.FormattedModelValue, new { type = "number", @class = "numericOnly"  })      
>   }
>    else
>    {
>     @Html.TextBox("", (object)Model,
>        new Dictionary<string, object>
>            {
>                { "id", ViewData.ModelMetadata.PropertyName },
>                { "name", ViewData.ModelMetadata.PropertyName },
>                { "class", "text-box single-line"},
>                { "data-bind", "value: " + ViewData.ModelMetadata.PropertyName },
>            })
>    }
>   
>     @Html.ValidationMessage(ViewData.ModelMetadata.PropertyName,
>        new Dictionary<string, object>
>            {
>                { "data-valmsg-for", ViewData.ModelMetadata.PropertyName }
>            })
></div>
>

>
>PhoneInfo template
>

>@model CardNumbers.Objects.PhoneInfo
>
><div id="PhoneInfo">
>    <div class="float-left">
>        @* @Html.EditorFor(model => model.Phone, EditorTemplate.TextBox)*@
>        <div class="editor-label">
>            @Html.LabelFor(model => model.Phone)
>        </div>
>        <div class="editor-field">
>            @Html.EditorFor(model => model.Phone)
>            @Html.ValidationMessageFor(model => model.Phone)
>        </div>
>    </div>
>    <div class="float-right">
>        @*@Html.EditorFor(model => model.Ext, EditorTemplate.TextBox)*@
>        <div class="editor-label">
>            @Html.LabelFor(model => model.Ext)
>        </div>
>        <div class="editor-field">
>            @Html.EditorFor(model => model.Ext)
>            @Html.ValidationMessageFor(model => model.Ext)
>        </div>
>    </div>
></div>
>

>
>And the ContactDetail template
>

>@using CardNumbers.Helper
>@model CardNumbers.Objects.ContactDetail
>
><div class="editor-label">
>    @Html.LabelFor(model => model.Contact)
></div>
><div class="editor-field">
>    @Html.EditorFor(model => model.Contact)
>    @Html.ValidationMessageFor(model => model.Contact)
></div>
>@*@Html.EditorFor(model => model.Email, EditorTemplate.TextBox)*@
><div class="editor-label">
>    @Html.LabelFor(model => model.Email)
></div>
><div class="editor-field">
>    @Html.EditorFor(model => model.Email)
>    @Html.ValidationMessageFor(model => model.Email)
></div>
>@Html.EditorFor(model => model.phoneInfo)