In Chrome and IE the clicking of the SELECT button for the uploads is kinda difficult when using MATERIAL skin. See the following video: https://www.screencast.com/t/VBe1zSss7c

How-to fix the bug:
1. Create a CSS file named dialog.css
2. Put the following class in the dialog.css file:

.RadUpload  .ruFileInput {
    height: 50px !important;
}

3. Set the DialogsCssFile property to point to the dialog.css file:

        <telerik:RadEditor ID="RadEditor1" Skin="Material" RenderMode="Lightweight" DialogsCssFile="~/dialog.css" runat="server">
            <ImageManager ViewPaths="~/Images" UploadPaths="~/Images" />
        </telerik:RadEditor>

4. Save the page.
5. Clear the browser cache and load the page in it. If needed reload the dialog contents 3-4 times to clear the cache -> right click and choose Reload frame from the Chrome context menu.