With the support of insert list command in Track Changes functionality, users can insert lists. Although with enabled tracking users are not able to delete the list items, but only the text inside.

Steps to reproduce:
http://demos.telerik.com/aspnet-ajax/editor/examples/trackchanges/defaultcs.aspx

1. Insert a list with enabled TrackChanges
2. Start deleting list items

Expected: The whole list item is removed
Actual: Only the text inside the list item is deleted

Under IE10 and 11 the CrossFade animation causes a random flickering. 

Creating a lists with sub list, navigating to a parent list item and trying to add an sibling list item will cause the list to break. 

On iOS 8 Safari the propagation of the "touch" event is not prevented, thus the element beneath the touched DropDownList item get touched as well.

When RenderMode is set to LightWeight and ToolbarMode is RibbonBar, a JavaScript error is thrown.

If a long paragraph is copied into the editor, <br> tags appear in thea content without being added at first place. 

For the time being you can resolve this by adding the following script below the editor declaration:

<telerik:RadEditor runat="server" ID="RadEditor1" StripFormattingOptions="AllExceptNewLines"></telerik:RadEditor>

<script type="text/javascript">
    var oldStripFormatting = Telerik.Web.UI.Editor.Utils.stripFormatting;

    Telerik.Web.UI.Editor.Utils.stripFormatting = function (textHtml, clearValue) {
        if (clearValue === "ALL_NO_BRAKES") {
            textHtml = textHtml.replace(/\n/g, "");
            textHtml = textHtml.replace(/<\/p>/g, "<br/>");
        }

        textHtml = oldStripFormatting.call(this, textHtml, clearValue);
        return textHtml;
    }
</script>

when trying to use the Visual Style Builder with IE 11, I get error

"System requirements not met

The Visual Style Builder requires a modern browser.

You can either upgrade Internet Explorer, or try Firefox for better experience on javascript-rich applications, such as this."

RadImageGallery fullscreen mode overrides viewport meta tag set on page.
If the user sets the following meta tag:

<meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1, maximum-scale=1.0, user-scalable=no, height=device-height" />

initially the page is not scalable. When the Gallery enters fullscreen mode, the page is zoomed out.
And when you exit fullscreen, the page stays zoomed out, the gallery proportions are changed and fonts are smaller.

The layout of these dialogs in SharePoint's Editor is broken to the point where the user would be unable to use them.