Create template T2, template T1, and host H. Link T1 to H. Create an item on T2. Link T2 to T1. Observe a bad database structure.

mysql> select h.hostid, h.host, itemid, i.name, key_, templateid from hosts h, items i where key_='agent.version' and h.hostid=i.hostid;
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3 rows in set (0.00 sec)

Note that both H's (hostid=21) and T1's (hostid=20) items refers to T2's (hostid=19) item in "templateid" column.