scp dos not work at all

I cannot get the scp protocol to work at all. Obviously support for ssh-agent is missing (MPARTIFACT-22) and I can only connect at all if I set the username, password, passphrase and privatekey of the repo. Unfortunately the deployment still fails with:

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jar:deploy:
[echo] maven.repo.list is set - using artifact deploy mode
Will deploy to 1 repository(ies): elsag
Deploying to repository: elsag
host: 'es3.elsag.de'
Using private key: C:\Dokumente und Einstellungen\jos\.ssh\id_dsa
Deploying: C:\Work\Projects\commons\test\project.xml-->elsag-commons/poms/elsag-test-0.2-SNAPSHOT.pom
deployNotCompressed=false
Executing command: scp -t /devel/maven/home/public_html/repo/maven-deployer-62294.zip
Executing command: unzip -u /devel/maven/home/public_html/repo/maven-deployer-62294.zip -d /devel/maven/home/public_html/repo

Failed to deploy to: elsag Reason: Cannot execute remote command: unzip -u /devel/maven/home/public_html/repo/maven-deployer-62294.zip -d /devel/maven/home/public_html/repo

org.apache.maven.deploy.exceptions.TransferFailedException: Cannot execute remote command: unzip -u /devel/maven/home/public_html/repo/maven-deployer-62294.zip -d /devel/maven/home/public_html/repo
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Executing the commend directly, it is obvious:

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$ ssh es3 unzip -u /devel/maven/home/public_html/repo/maven-deployer-62294.zip -d /devel/maven/home/public_html/repo
Archive: /devel/maven/home/public_html/repo/maven-deployer-62294.zip
replace /devel/maven/home/public_html/repo/elsag-commons/poms/elsag-test-0.2-SNAPSHOT.pom? [y]es, [n]o, [A]ll, [N]one, [r]ename: Killed by signal 2.
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Please use -uo as option for unzip! Overwriting is quite common for SNAPSHOT

– Jörg