Thank you for your message.
First of all I would like to point out that the Forums are obsolete and they will be locked soon, please post your question to a Question and Answers section.
Regarding your issue - I was unable to reproduce it on my instance. I was testing it on our sample corporate site under Examples -> Web parts -> Listing and viewers -> Custom query -> Uni. viewer with custom query.
This query is displaying basically the menu structure. Once I went to some page, lets say Partners and then went to Form tab and changed the letter to be low case and saved the uni viewer displayed it correctly. I dont see any reason why it would convert the letter to upper case.
The default transformation is using this to get values:
<%# HTMLHelper.HTMLEncode(Convert.ToString(Eval("MenuItemName"))) %>
I recommend you to try this on our sample corporate and see how it works. If you are able to reproduce it there, please let us know.