Specified specific snapshot version for a plugin is ignored

When a snapshot version in the form 1.0-yyyymmdd-hhmmss is specified,
the 1.0-SNAPSHOT version (installed in local repo) is used.

When a pluginRepository is specified, m2 will mark it as resolved,
but still use the snapshot version:

[DEBUG] maven-xdoclet-plugin: resolved to version 1.0-20050918.153058-2 from repository fire
[DEBUG] maven-plugin-parent: using locally installed snapshot
[DEBUG] maven-xdoclet-plugin: resolved to version 1.0-20050918.153058-2 from repository fire
[DEBUG] org.apache.maven:apennine-ejb:ejb:1.0-SNAPSHOT (selected for null)
[DEBUG] org.apache.maven.plugins:maven-xdoclet-plugin:maven-plugin:1.0-SNAPSHOT (selected for runtime)