win 8, 64 bit, java 64, latest version
I have been experiencing the appearance of large rectangles 'holes' that go to bottom of world. They are not empty, but filled with invisible blocks of some kind. If you go in them you are trapped and have to die to escape. This is in survival mode, single player.
My current world has at least 4, with one appearing very near my home base yesterday., (See image) I tried to wall it off so I wouldn't fall in but when I went back to my home area random blocks had appeared new a glass underwater bridge I had made. And inside that glass tunnel were invisible blocks I couldn't walk through.
I had read that using tnt on a whole would make it visible so went back to where I had made the wall, set up some tnt and detonated that. Didn't make it visible but for some reason the invisible blocks in tunnel were gone.
One of my rooms is made of glass and extra glass blocks had appeared that did not go away when broken. However after the tnt experiment and reloading the game they did go away. Close to the hole - but not in it of course, blocks do not disappear when dug up or broken.
Texturepacks do not seem to affect it.
This is a real issue folks - I spent a lot of time building, creating etc etc. weeks at least. And this is the second world this has happened to.