Using the break key should make you stop moving. However, it doesn't seem to use your real directional thrust but always the normal thrust - mass value like before.
Easy to reproduce:
# accelerate forwards to max speed
# redistribute everything to a different thrust direction
# use break key
# you can break just fine, even though you don't have any thrust available in that direction you're going (unless you rotate the ship correctly but well, you didn't in this case)
# accelerate in any direction
# redistribute everything to 100% rotational direction
# use break key