I created a few custom regexp on zabbix server to filter some items, everything is working as expected for servers monitored by zabbix agents that are connected directly to my zabbix server, I can see on the debug logs that the agent downloads from the server the regular expression definition (@LOGON for example).
This doesn't seem to happen for zabbix agents which communicate to the zabbix server through a zabbix proxy, it seems zabbix proxy doesn't request the regular expression definition and in this way, the filters on the agents are broken.
Right now I can't update the zabbix proxy or zabbix agentd to 1.8.3 but I haven't read anything about changes in the regular expressions betweeen 1.8 and 1.8.3 (read on the "What's new in Zabbix...")