Puppet agent can't clear a stale agent_catalog_run.lock file

System: Debian 6 (ARM)
Reproducible: yes
Steps:
1. Start puppet agent on client ( 'service puppet start' )
2. Fill /var to 100%
3. Run 'puppet agent --test'
4. Note error message: 'Notice: Run of Puppet configuration client already in progress; skipping (/var/lib/puppet/state/agent_catalog_run.lock exists)'
5. Clear space on /var
6. Try 'puppet agent --test' again
7. Error message persists until .lock file is manually removed