Some more information regarding my problem:
It seems that the loadXML and saveXML does not like the data binding.
When I don't use a data connection (and no binding), navigation works perfect and the data on the different pages is stored.
When I use a data connection, the navigation still works, but the data is not stored anymore.
When I use a data connection and a data binding, navigation does not work and also the data is not stored.
By the way: I am using Lifecycle Designer 7.