I found that the blocks used to create a beacon hill, and the beacon itself, became unbreakable. They appear to have the same properties as blocks in the protected zones on SMP. I am running on a single player survival so cannot see why this has happened.
MC-30288
Unbreakable Beacon+Pyramid
Resolved
Cannot Reproduce
0
Unable to reproduce. Please force a crash by pressing F3 + C for 10 seconds while in-game and attach the crash report (
[minecraft|http://hopper.minecraft.net/help/finding-minecraft-data-folder]/crash-reports/crash-<DATE>-client.txt) here.