[chef] Validation key file empties and new copy is created

[Millisami < >]

After installing chef 10.12.0 and doing knife bootstrap, the validator key is
emptied and a new one is created.
e.g.

The pem my-validator.pem is emptied and a new file my-validator.1340601879.pem
is created with the contents of the my-validator.pem

Why is this weird behaviour?