I am trying to use ui:inputDate in our lightning component and noticed quite annoying behaviour of DatePicker. When you first time attempt to use field with ui:inputDate the page jumps. On second attempt, it works perfectly. I found the same problem with ui:inputDate when I tried to create New Task in Opportunity. To reproduce it you need to put a scroll bar at top position on an Opportunity page.
After that choose Due Date and the page jumps.
Is it a bug?