When I started Minecraft for the first time after 1.8.0 and accepting the update I started my world but instead of starting when I left off it put miles away on a elevated rail I had created but hadn't been at for sometime and I immediately died. When I respawned I was back at my base where I expected to have started. I tried to find where on the rail system I died but it's very extensive and I haven't been successful. Fortunately for me I had previously exported that game before the update. I was able to import and it was fine.

The only difference between the 2 games was: the one the bug occurred on I changed to the default resource pack.

I had been on vacation and while traveling using my Surface Book the update occurred and I had no issue with loading an existing game with changing the resource pack to the default (a practice I do with updates).