Using the "message signing" feature in the Bitcoin and Dash it's static with the same message. Signing the same message with the same private key will result always in the same signature.

This behavior is not the same in Peercoin or in the old wallet of Bitcoin. In these wallets, the signature changes even if both messages are equal, for me it has some "nonce" inside.

Example:

Message: xxx

Address: 18ZbyqYYwgEmn5hVMtJpihPeYxsUpCLhr7

Bitcoin 0.8.5-beta:

INbwudFmql3iOH6c1UWylOpgLu5zrrqGrcFCanirz+Zb/nmJkcDXSkug5J0s3Yawb1/GzZKqXVjRHRNVSenRdMI=
II7W5su7EBQ4u1ppSKMVcmy8etnJsSOsvQHZ3j+moJs2P/vjwpqMlZkvOQ+W5odCdmwOz/5wK2T0RDV6aiqaEQs=
H7XNf5of1kmpwvcvLqVKIYc3TY5eN3kIrZWJPlDYhKVZekZ7Xk2qnJWjNDdsODkYtLEYn5p6fJfIC9LR+/rQky0=

Bitcoin 0.14.2:

IBl6SRpJwzGjXTDbO/IuUcHzlbxqbzN+MmeGRLRIAcPjKpQ9XgQG+gBOzo5PcgtBbtDqXhJIKnbUH9vEcQ5CNlM=
IBl6SRpJwzGjXTDbO/IuUcHzlbxqbzN+MmeGRLRIAcPjKpQ9XgQG+gBOzo5PcgtBbtDqXhJIKnbUH9vEcQ5CNlM=
IBl6SRpJwzGjXTDbO/IuUcHzlbxqbzN+MmeGRLRIAcPjKpQ9XgQG+gBOzo5PcgtBbtDqXhJIKnbUH9vEcQ5CNlM=

In the old Bitcoin-qt the same message with the same private key create different signatures. But in the new Bitcoin-qt it's result in the same signature.

What is the difference between this signature method? Have an alternative to continue getting the PK from a signature in the second case? Have name of this specific change?