I tested my 4K disc, playing from the 40 minute to 52 minute marks. The disc played fine on my Panasonic 820 player. I will watch the entire film later, but wanted to make sure I didn't have a defective disc that needed returned.
You will need to open the set when it arrives, as you need to send back just the BD in order to get a replacement -- unless you have some magic way of removing that disc without opening the package. ;)