Steps to reproduce:

1. create active agent item with key log[/tmp/str.log,"ERR: (.)", ,,,\1] and value type text
2. assign the owner host to a proxy
3. do echo 'ERR: 1' >> str.log and observe that while proxy accepts agent data, no value is transferred to server.

If host is monitored directly or item value type is changed to log the monitoring starts working.