Versions Maven Plugin does not update Parent POM

Question

I have a strange problem with the Versions Maven Plugin. I released yesterday a new version of a my Ueber Parent. Now I would like to update several other POMs which use a previous snapshot version of this parent.

Without having a ~/.m2/settings.xml running mvn versions:update-parent does not update the used parent to the latest release of it. I don't understand why?

An example POM might look like this:

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                             http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>com.buschmais.jqassistant</groupId>
        <artifactId>jqa-uber-parent</artifactId>
        <version>1.2.0-RC2-SNAPSHOT</version>
    </parent>

    <repositories>
        <repository>
            <snapshots><enabled>true</enabled></snapshots>
            <id>sonatype-nexus-snapshots</id>
            <name>Sonatype Nexus Snapshots</name>
            <url>https://oss.sonatype.org/content/repositories/snapshots</url>
        </repository>
    </repositories>
</project>

The crazy stuff is if I add Maven central repository explicitly to the POM the latest released version of the parent POM is found by the Versions Plugin.

<repository>
    <id>central</id>
    <url>https://repo1.maven.apache.org/maven2</url>
</repository>

Does any one know why?