I was in the end and i was playing around in f5 mode and if i turned my camera to a certain position i could see through the walls. I don't know if it works in other places but people can use this as an exploit if anyone else finds it. Also if you look at the sidebar i was playing around with an NBT editor so ignore that.
Thank you for your report.
However, your ticket has been resolved as a duplicate.
This issue has been linked to the original bugreport: MC-63070. You can find or add further information on that report.
Please search before reporting any bugs, as it's likely that one exists already.