Up until now, it has always been possible to mix different case parameters of the same name in a family. You could have a parameter called 'T' and one called 't' and it would sit very happily.
It now appears to be a different case in Revit 2014 and this has been swept away. It's not actually apparent with existing families until they are loaded into a project, taking you from this:
In hindsight, it's probably not best practice to have parameters named in this way. I'm guessing we'll just have to take our medicine and get on with it!