Problem with the signature of medner-artifact

Also tried reording the arguments to mender-artifact sign, still looks ok to me:

$ mender-artifact sign my-container-update-1.0.mender -k private.key -o my-container-update-1.0-signed.mender
$ mender-artifact read my-container-update-1.0-signed.mender -k public.key 
Mender artifact:
  Name: my-container-update-1.0
  Format: mender
  Version: 3
  Signature: signed and verified correctly
  Compatible devices: '[my-device-type]'
  Provides group: 
  Depends on one of artifact(s): []
  Depends on one of group(s): []
  State scripts:

Updates:
    0:
    Type:   docker
    Provides: Nothing
    Depends: Nothing
    Metadata:
	{
	  "containers": [
	    "debian@sha256:e25b64a9cf82c72080074d6b1bba7329cdd752d51574971fd37731ed164f3345"
	  ]
	}

I was using:

$ mender-artifact -version
mender-artifact version 3.1.0-dirty