updated to 4.3 a few days ago and noticed a few UI issues that caused me to go back to 4.2.
Issues i found were the following:
clicking on UI buttons such as the local/world orientation, widget swaps and snapping tools.
Had the error of not showing any options via dropdown list.
Right clicking in BP’s event graph to search for nodes did appear either.
sounds like a window popup animation error of some kind
Hope this helps