Hi Jason. You're right, but in my case something happens at the mvc controller side. Say you have a controller like:

using System.Web.Mvc;

namespace MyNamespace
{
public class TestHtmlEditorController : Controller
{
[ValidateAntiForgeryToken]
[HttpPost]
public ActionResult SaveTestHtmlEditor(string MyString)
{
var myDecodedString = System.Web.HttpUtility.UrlDecode(MyString);
return Content("SUCCESS!");
}

[HttpGet]
public ActionResult GetTestHtmlEditor()
{
return View("TestHtmlEditor");
}
}
}

And a view like:

@using Infragistics.Web.Mvc

@{
ViewBag.Title = "TEST HTML";
}

@using (Html.BeginForm("SaveTestHtmlEditor", "TestHtmlEditor", FormMethod.Post, new { id = "TestForm" }))
{
@Html.AntiForgeryToken()
@Html.ValidationSummary(true)

@(Html.Infragistics().HtmlEditor()
.ID("MyString")
.InputName("MyString")
.Height("150px")
.Width("100%")
.ShowTextToolbar(false)
.ShowInsertObjectToolbar(false)
.ShowFormattingToolbar(true)
.ShowCopyPasteToolbar(false)
.Render())
<p />

<div id="divSaveEnd" style="margin-top: 20px;">
<input type="button" id="saveData" class="button" onclick="saveForm()" value="Aceptar" />
</div>
}

<script type="text/javascript">

function saveForm() {
$.ajax({
url: '@Url.Action("SaveTestHtmlEditor", "TestHtmlEditor")',
type: "POST",
data: $("#TestForm").serialize()
});
}

</script>

Type something like "HELLO + WORLD" and check out MyString and myDecodedString. You will see that "+" is not encoded in MyString and UrlDecode removes it :(

Thank you for this update. Using the information I was able to reproduce the behavior. Looking in to this further, the value of the igHtmlEditor is getting encoded through the use of encodeURI which ignores special characters like the plus sign. We should probably be using encodeURIComponent, but I'd like to have the team take a look at this a bit further to get more information about why we are using encodeURI. I have created a development issue for this with an ID of 189760 and have created a support case that you will be able to use to track this issue.