Mobility of ubiquitous systems offers the possibility of using the current context to infer information that might otherwise require user input. This can either make user interfaces more intuitive or cause subtle and confusing mode changes. We discuss the analysis of such systems that will allow the designer to predict potential pitfalls before the design is fielded. Whereas the current predominant approach to understanding mobile systems is to build and explore experimental prototypes, our exploration highlights the possibility that early models of an interactive system might be used to predict problems with embedding in context before costly mistakes have been made. Analysis based on model checking is used to contrast configuration and context issues in two interfaces to a process control system.