M1 deploy blows away local repository metadata

Steps to reproduce:

1) Bind maven-one-plugin:deploy-maven-one-repository to the "deploy" phase (and add suitable configuration).
2) Run "mvn deploy" on a project
3) After the deploy finishes, look at maven-metadata.xml for the project in the local repository.
4) Note that the file has been overwritten with invalid contents.

In particular, the local repository metadata has been overwritten by the file legacy_repo/$

/poms/maven-metadata.xml. Unfortunately, because of the way M1 repositories are structured, this file contains version numbers for all artifacts in the group. I'll attach mine in a moment as an example.

This effectively corrupts the local repository. Subsequent builds that depend on the affected project will fail because they're looking for phantom version numbers that don't exist.

Note: we recently switched to the WebDAV wagon for deployment, and this bug seemed to show up at about the same time. The two could be related, or it could just be a red herring...