I just ran into an issue on 8.1.3 that I hadn’t seen before. A client wanted the time zone control added to the Contact details screen, that normally resides on the Details tab. We were experiencing strange things when testing the Contact screen, where the progress bar indicator never stopped working. It turns out that having a Timezone control loaded twice on the same page was throwing java script errors in the underlying dojo code because it was trying to instantiate objects that already existed due to the other control. This only happened when the Details tab was active as it then tried to render both controls (The Contact Detail version and the Details tab version).
The solution was to remove the control from the Details tab so it only existed one time.