Dev Express validation message not showing within .NET WebBrowser control

Question

I am working with a legacy .NET application that uses a System.Windows.Controls.WebBrowser control. I have full source code access to a .NET MVC web application that is exposed through this WebBrowser control. Of course, the MVC web app is also available via a normal web browser (in my case, IE 11).

The MVC app uses DevExpress 15.1.5 for many of it's UI components, and I am having some issues with rendering/behavior differences between the WebBrowser control rendered "version" and the IE 11 "version" of the application. The main issue I'd like to resolve is that dev express validation messages do not appear in the WebBrowser rendering, but they do appear in the IE 11 rendering. Here is an example:

 <td class="">
  @Html.DevExpress().SpinEditFor(x => x.SomeRange,
    settings => {
    settings.Name = "SomeRange";
    settings.Properties.MinValue = 0;
    settings.Properties.MaxValue = 100;
        settings.Properties.NullText = "Some Range";
    settings.Properties.NumberType = SpinEditNumberType.Integer;
 }).GetHtml()
</td>

When a user enters a value greater than 100, in the IE 11 rendering, they are presented with an validation message that says:

The number must be in the range 0...100

However, when a user performs this in the WebBrowser control version, no message is displayed.

The WebBrowser is, with certainty, rendering with IE 11 document mode. I have verified this by forcing it to do so via the registry settings mentioned here, and checking the document.documentMode in both WebBrowser and IE 11 to verify they are both the same (and they were, both return 11).

Legacy App (WebBrowser Control)
appName:        Netscape
appVersion:     5.0 (Windows NT 6.2; WOW64; Trident/7.0; rv:11.0) like Gecko
documentMode:   11 

IE 11
appName:        Netscape
appVersion:     5.0 (Windows NT 6.3; WOW64; Trident/7.0; .NET4.0E; .NET4.0C; .NET CLR 3.5.30729; .NET CLR 2.0.50727; .NET CLR 3.0.30729; rv:11.0) like Gecko
documentMode:   11 

Notably, there are some other slight rendering differences between the two, for example I noticed that default no-css <button> elements are styled slightly differently (a WebBrowser <button> looked like it may have been from IE 7).

I'm not so worried about the rendering differences (I only notice differences on default un-styled controls) but I do need the validation messages to appear. Any idea on what to check next, or how to resolve this?