Game froze for a brief moment before crashing. Upon reloading my world I found that every block within a few blocks of me was reset to the 'default'.

That is, every block within about a five block radius of me that I had placed was deleted, and instead replaced by the default blocks of dirt and bedrock (the world was a default superflat world). The game crashed after I had broken a jukebox I had just placed with an animated texture containing two frames.