By convention, all lowerCamelCased methods are translated into UpperCamelCased in C#, so unles in very specific and limited cases, between Ext JS client side and Ext.NET server-side naming convention for public members will be like this.
In other words:
Ext.NET / server side / C#: UpperCamelCase
Knowing this, it may be easier to "translate" what you read when you think either client-side or server-side when speaking about Ext.NET. :)
Hope this helps.
EDIT: I see, you were talking about the [b]UI[b] bit of the method not being Ui
(all uppercase). Microsoft has a similar rule where names with just two characters may be full upper cased, whereas others should be camel cased, as System.IO and System.Uri.