The issue is resolved and the fix will be available in Q1 2015.

The following workaround could be used as a temporary solution:

<telerik:RadEditor ID="RadEditor1" runat="server" OnClientLoad="OnClientLoad">
<Content>
text <input type="button" value="button1"></input> text<br />
text <input type="button" value="button2"></input> text<br />
text <input type="submit" value="button3"></input> text
</Content>
</telerik:RadEditor>

<script type="text/javascript">
function OnClientLoad(editor, args) {
var isIE11 = $telerik.isIE10Mode && !$telerik.isIE10;
if ($telerik.isFirefox || $telerik.isSafari || isIE11) {
var $E = Telerik.Web.UI.Editor;
var eventType = $telerik.isFirefox || isIE11 ? "mousedown" : "mouseup";
$telerik.$(editor.get_contentArea()).on(eventType, "input:button", function (e) {
var range = new $E.DomRange(getBrowserRange(editor));
range.selectNode(e.target);
range.select();
});
}
}

function getBrowserRange(editor) {
var selection = editor.getSelection();
var range = selection.getRange(true);
if (!range) {
editor.setFocus();
range = selection.getRange(true);
}
return range;
}
</script>