I've noticed that if I an edit has been made to a notebook, which can be accidental when opening a notebook in developer mode, Fabric caches the users changes when the browser is closed. If an update occurs from version control (pull request or an undo) these intended updates get overwritten by the cached version when the notebook is reopened in the browser! This was unexpected. One must then click on a popup warning and choose to accept the other version to ditched this cached version.