Steps to reproduce:

1. Navigate to Configuration of items/triggers of "Zabbix server";
2. Check one or more items/triggers belonging to Mounted filesystem discovery;
3. Click Mass update;
4. Do some changes, e.g. change Item type to SSH agent or add a new tag for triggers;
5. Click Update.

Result:
Frontend shows green box saying that item/trigger was "successfully updated".

Expected:
Configuration of items/triggers hasn't changed at all.