deployed snapshot name has different build numbers for multiple artifacts of the same build

An example POM or at least the relevant lines from the log output where Maven prints what it deploys would be helpful.

[04:41:21]: [INFO] [deploy:deploy

]
[04:41:21]: [INFO] No primary artifact to deploy, deploy attached artifacts instead.
[04:41:21]: [INFO] Retrieving previous build number from snapshots_repo
[04:41:21]: Uploading: file:////build/m2repository/snapshots/myapp/testutils/11.6-SNAPSHOT/testutils-11.6-20090902.084121-24.jar
[04:41:21]: 78K uploaded (testutils-11.6-20090902.084121-24.jar)
[04:41:21]: [INFO] Retrieving previous metadata from snapshots_repo
[04:41:21]: [INFO] Uploading repository metadata for: 'artifact myapptestutils'
[04:41:21]: [INFO] Retrieving previous metadata from snapshots_repo
[04:41:21]: [INFO] Uploading repository metadata for: 'snapshot myapp:testutils:11.6-SNAPSHOT'
[04:41:21]: [INFO] Retrieving previous build number from snapshots_repo
[04:41:21]: Uploading: file:////build/m2repository/snapshots/myapp/testutils/11.6-SNAPSHOT/testutils-11.6-20090902.084121-25.resource
[04:41:21]: 2K uploaded (testutils-11.6-20090902.084121-25.resource)
[04:41:21]: [INFO] Retrieving previous metadata from snapshots_build
[04:41:22]: [INFO] Uploading repository metadata for: 'artifact myapp:testutils'
[04:41:22]: [INFO] Retrieving previous metadata from snapshots_repo
[04:41:22]: [INFO] Uploading repository metadata for: 'snapshot myapp:testutils:11.6-SNAPSHOT'
[04:41:22]: [INFO] ------------------------------------------------------------------------
[04:41:22]: [INFO] BUILD SUCCESSFUL

I am using project.addAttachedArtifact(artifact); in my mojo to attach the artifact

Pom for distribution management:
<distributionManagement>
<repository>
.........
</repository>
<snapshotRepository>
<id>snapshots_repo</id>
<name>snapshots_repo</name>
<url>file:////build/m2repository/snapshots</url>
</snapshotRepository>
</distributionManagement>

I am using project.addAttachedArtifact(artifact); in my mojo to attach the artifact

That's a valuable piece of info. Could you try calling MavenProjectHelper.attachArtifact() instead of directly mutating the project? Use something like

/**
 * @component
 */
private MavenProjectHelper projectHelper;

to get the component injected into your mojo.

I tried that .
if i use MavenProjectHelper.attachArtifact() the artifacts do not have timestamp or build number. They get deployed the same way as using uniqueVersion=false.
The reason why I didn't use MavenProjectHelper the first time is that for some projects I needed to create artifacts with a different name than project.name, and there is no MavenProjectHelper.attachArtifact() that would accept artifactId as parameter.
Also I couldn't (still can't) use AttachedArtifact in project.addAttachedArtifact(artifact) as it is used in MavenProjectHelper because of some dependency conflict (I use gmaven 1.0-rc-4 and maven 2.2.1) and I used instead DefaultArtifact. I guess that is not a problem since they both implement Artifact.

Fixed case of broken timestamped versions via attachArtifact() in r963122.

Calling MavenProject.addAttachedArtifact() directly isn't the intended API usage so if you want to go down that route I suggest to implement your own versions of AttachedArtifact as well.