When using puppet-agent-5.3.3 to upgrade itself to puppet-agent-5.3.4, during the upgrade process there's error output from ruby, related to fast_gettext:
That only happens on the upgrade itself. Afterward, the 5.3.4 agent seems to be fine.
Note, though, that if there are other pending changes during the agent run when 5.3.3 upgrades to 5.3.4, the other changes are not applied (the agent run errors out) until the 5.3.4 agent is run again.
This is probably a matter for the release notes or documentation more than anything.