The problem is not whether the html markup is lower or uppercase. The HtmlTextBox (as browsers) handle both cases, the problem is that currently we only handle the case when the closing "/" is missing for lowercase markup i.e.
- if you have <br> we would replace it with <br/> and parse the html correctly
- if you have <BR>, the replace action would not kick in and therefore the error. We would be able to handle uppercase for subsequent versions.
As for the RadEditor, I just checked the "HTML" view of this ticket reply and I see that it has generated lowercase <br/> tags with closing "/", so I am not sure how you've got the uppercase ones without closing "/". If you've somehow managed to do that, you can contact my colleagues from RadEditor's team for more info.
the Telerik team