portage package provider does not respect package versions

The portage package provider does not respect versioning of packages, so one can't define specific versions of packages to install via puppet agent.

As a result, on every run the puppet agent tries to install a specific version when another not defined version is installed, but effectively does only ensure that the package is installed via 

emerge example/package

Desired should be that the agent installs the defined version via 

emerge =example/package-1.2.3-r4