nexus-staging-maven-plugin refuse to upload after deferred deployment

Question

I have a multi-module project that has nexus-staging-maven-plugin configured in parent pom.xml:

        <plugin>
            <groupId>org.sonatype.plugins</groupId>
            <artifactId>nexus-staging-maven-plugin</artifactId>
            <version>1.6.6</version>
            <extensions>true</extensions>
            <configuration>
                <serverId>ossrh</serverId>
                <nexusUrl>https://oss.sonatype.org/</nexusUrl>
                <!--<autoReleaseAfterClose>true</autoReleaseAfterClose>-->
            </configuration>
        </plugin>

By default it should be inherited by all submodules (except those disabled using technique in How to disable nexus-staging-maven-plugin in sub-modules)

However, when I start deployment:

mvn clean deploy -DskipTests=true -Prelease-sign-artifacts -Dgpg.passphrase=*****

I see the following message:

[INFO] Installing Nexus Staging features:
[INFO]   ... total of 5 executions of maven-deploy-plugin replaced with nexus-staging-maven-plugin

...

[INFO] --- nexus-staging-maven-plugin:1.6.6:deploy (injected-nexus-deploy) @ spookystuff-core ---
[INFO] Performing deferred deploys (gathering into "/home/peng/git/spookystuff/target/nexus-staging/deferred")...
[INFO] Installing /home/peng/git/spookystuff/core/target/spookystuff-core-0.3.2-SNAPSHOT.jar to /home/peng/git/spookystuff/target/nexus-staging/deferred/com/tribbloids/spookystuff/spookystuff-core/0.3.2-SNAPSHOT/spookystuff-core-0.3.2-SNAPSHOT.jar

...

[INFO] Reactor Summary:

...

[INFO] BUILD SUCCESS

No upload happens whatsoever. The artifact that should be uploaded to nexus were still cached under:

/target/nexus-staging/deferred

but neither the log nor nexus server record indicates that it has been uploaded. What has been wrong here and what should I do to fix it?