While placing and breaking redstone (or redstone torch) while it's being powered and connected to a piston, the block underneath (in my case dirt) redstone was being broken everytime redstone was destroyed. After a couple of repeats, the block was destroyed.

 HOW TO RECREATE:
Place still water source 4x4x1 behind a torch. Connect it with redstone powder to two pistons and start rapidly breaking and placing again redstone or the torch.

Note: Don't stand on the supporting block.