I was once doing a lot of stuff to a disk with gnu parted. I popped out and popped back in like this:

  $ parted
  <do a lot of work>

whoops, all the I erased and recreated were... my root disk!

I couldn't figure otu the partition table of the running disk, but I was able to rsync all the data elsewhere and recover it.

IMHO if you invoke parted - WITH NO ARGUMENTS - it should not make a choice for you.