User Interface (UI) development is challenging as modern UIs are expected to be available for a wide-range of diverse and constantly changing contexts including various (mobile) platforms, users, and environments. Model-Driven Engineering (MDE) principles have been successfully applied to UI development, resulting in a clear separation into multiple UI models on different levels of abstraction. While this addresses many challenges involved in UI development, it also poses an additional challenge: ensuring that all the different UI models remain consistent during their development and maintenance. In this paper, we argue that this consistency related challenge has not yet been adequately addressed, and identify consistent UI development as a new and promising application domain for existing and future research on bidirectional transformations.