I use UML (or sth similar to UML :)) when I talk to friends about something we're about to do. To discuss ideas. Not to prepare UML project that will autogenerate code for me. I can't imagine creating my classes in UML then generate code and not tweak it later. This never happens. So you will have to bring changes from code to UML. And when I use UML I draw on whiteboard or paper. Never in tool like Enterprise Architect.

The only reason to document my whole code in UML would be a contract where client demands it. For example when he want's to have an option to change software shop after part of software was finished.