Domino Designer does not always update the source code nor does it always make it obvious that an error exists within your XPage code.
This nasty little issue, although infrequent, can result in a great deal of time wasted when you are making changes and wondering why your XPage is not working the way you think it should.
If you are not a “source coder” (most of us aren’t), make it a habit to check the source right away if things are going unexpectedly awry.
I've had this happen to me before and its so frustrating! It seems to happen to me more when I have been working in the source view for a while and then try to go back to the design view.
It can be really frustrating. Sometimes XPages are frustrating enough without your code not actually being updated when you change it!