The two lines that are output of this command:

# foreman-rake -- config -k rss_enable
API controllers newer than Apipie cache! Run apipie:cache rake task to regenerate cache.
false

are both printed to stdout. Whereas this might be okay for humans, it makes the life of some programs harder, like the foreman_config_entry type/provider shipped by https://github.com/theforeman/puppet-foreman. There's detailed information about why this is an issue here:

https://github.com/theforeman/puppet-foreman/issues/989

It'd be nice if Apipie warnings produced by apipie.rb (https://github.com/theforeman/puppet-foreman/issues/989) were send to stderr instead.