On the launchContext extension documentation, add the following: Variables made available by launch context may be used by any expression within the Questionnaire, however they are most safely used within initialExpression.  Because the launch context might vary each time the QuestionnaireResponse is opened or edited, by populating launchContext into the values of (possibly hidden) questions via iniitalExpression, the 'original' context in which the QuestionnaireResponse was created can be retained.