When Maven runs Java 6, maven-metadata.xml file is "corrupted"

When you run Maven under Java 6, the "maven-metadata.xml" file that gets written to the remote repository is markedly different from the one generated under Java 5 and earlier. This file is "corrupted" in the sense that Maven reports errors about it, and might not be able to locate snapshots as a result. See attachment for an example file; you'd expect to see build numbers or -SNAPSHOTs, but not both at once.

This issue is described further at http://www.nabble.com/Maven-and-JDK-1.6-t3060866s177.html (originally message only, not the followups). This might be related to MNG-2709, but I don't think it's a duplicate, as it has nothing to do with testing or parents.