Well you said - may be not in these exact terms because I don't have the thread either -
"afaics, you sign the same message - you get the same signature."
Those who don't have a cryptographically secure random number generator might use SHA384(signedMessage) for that. In this case you'll be getting the same signature again and again and again...
PS: BTW, why people use random number generators for that? It's harder to generate a truly random number than to calculate hash(signedMessage).
PS2: Disregard "PS", more likely it's because some of these people might use a random number generator with NSA backdoor. This reminds me something...
Bitcoin core was using a random k, therefore the signature from the blockchain is using one. It's not going to match one produced by a deterministic hash of the message.