Maven release plugin: specify java compiler version

I have this project made of multiple jars and war to make an ear. I build everything in snapshot and it works great. Then I made a release for every single project and saw that the jars and the war were slightly different in size than the snapshot ones.

Comparing file to file I realized that the .class files were all there, but slightly larger or bigger, nothing more than 40 bytes generally.

I force compilation to use java 1.5 using this tag in Maven:

<build>
    <pluginManagement>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.0.2</version>
                <configuration>
                    <source>1.5</source>
                    <target>1.5</target> 
                </configuration>

I use this tag for the release plugin:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-release-plugin</artifactId>
    <version>2.0</version>
    <configuration>
        <releaseProfiles>release</releaseProfiles>
        <goals>deploy</goals>
    </configuration>
</plugin>

Could it be that the release plugin is compiling in 1.6 or other, explaining the classes size difference ? If so can I make the release plugin compile in 1.5 ?

Thanks for your input.