Maven jarsigner plugin not working during release

I need to sign the released jars, and I want to do this with the maven jarsigner plugin. So I added the following:

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-jarsigner-plugin</artifactId>
            <version>1.2</version>
            <configuration>
                <archive>target/${myarchive}.jar</archive>
                <keystore>${key.location}</keystore>
                <storepass>${keypass}</storepass>
                <alias>${key.alias}</alias>
                <verbose>true</verbose>
            </configuration>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>sign</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>

I provide the missing options on the command line.

When I start mvn install, everything works fine and the archive is signed. But when I run release:prepare release:perform, the jarsigner plugin fails: the 'Parameter alias' for the target org.apache.maven.plugins: maven-jarsigner-plugin: 1.2: the sign is missing or invalid

When I run in debug mode, I see the following:

For mvn install:

[DEBUG] Configuring mojo org.apache.maven.plugins:maven-jarsigner-plugin:1.2:sign from plugin realm ClassRealm[plugin>org.apache.m
aven.plugins:maven-jarsigner-plugin:1.2, parent: sun.misc.Launcher$AppClassLoader@6d6f0472]
[DEBUG] Configuring mojo 'org.apache.maven.plugins:maven-jarsigner-plugin:1.2:sign' with basic configurator -->
[DEBUG]   (f) alias = myalias
[DEBUG]   (f) archive = myarchive
[DEBUG]   (f) arguments = []
[DEBUG]   (f) keystore = mykeystore
[DEBUG]   (f) processAttachedArtifacts = true
[DEBUG]   (f) processMainArtifact = true
[DEBUG]   (f) project = MavenProject: com.playtech.chat:ums_supportchatapplet:12.4-SNAPSHOT @ *********\pom.xml
[DEBUG]   (f) removeExistingSignatures = false
[DEBUG]   (f) skip = false
[DEBUG]   (f) storepass = changeit
[DEBUG]   (f) verbose = true
[DEBUG] -- end configuration --

But when I run release:prepare release:perform, I see:

Configuring mojo org.apache.maven.plugins:maven-jarsigner-plugin:1.2:sign from plugin realm ClassRealm[plugin>org.apache.maven.plugins:maven-jarsigner-plugin:1.2, parent: sun.misc.Launcher$AppClassLoader@553f5d07]
[INFO] [DEBUG] Configuring mojo 'org.apache.maven.plugins:maven-jarsigner-plugin:1.2:sign' with basic configurator -->
[INFO] [DEBUG]   (f) archive = myarchive
[INFO] [DEBUG]   (f) arguments = []
[INFO] [DEBUG]   (f) processAttachedArtifacts = true
[INFO] [DEBUG]   (f) processMainArtifact = true
[INFO] [DEBUG]   (f) project = MavenProject: com.playtech.chat:ums_supportchatapplet:12.4.0.1 @ *****\pom.xml
[INFO] [DEBUG]   (f) removeExistingSignatures = false
[INFO] [DEBUG]   (f) skip = false
[INFO] [DEBUG]   (f) verbose = true
[INFO] [DEBUG] -- end configuration --

Therefore, with the exception of the property archive, other properties are ignored at release time.

Any ideas are much appreciated.