Configuration -> Hosts
Select some/all hosts
Select and execute "mass delete" action.

get following error:

Graph prototype "gr333" deleted.
Graph prototype "gr333 2" deleted.
Graph prototype "gr333" deleted.
Graph prototype "gr333 2" deleted.
Graph prototype "gr333" deleted.
Graph prototype "gr333 2" deleted.
Graph prototype "kk" deleted.
Deleted: Trigger prototype "123" on "host 10, exp host".
Deleted: Trigger prototype "asd" on "exp host".
Deleted: Item prototype "asd" on "exp host".
Deleted: Item prototype "ditem" on "Disc host".
Deleted: Item prototype "ditem" on "Disc host 2".
Deleted: Item prototype "ditem" on "Disc host 3".
Deleted: Item prototype "ditem" on "Disc host 4".
Deleted: Discovery rule "asd" on "exp host".
Deleted: Discovery rule "drule" on "Disc host".
Deleted: Discovery rule "drule" on "Disc host 2".
Deleted: Discovery rule "drule" on "Disc host 3".
Deleted: Discovery rule "drule" on "Disc host 4".
Deleted: Graph "aaa" on "host 1".
Deleted: Graph "aaa" on "asd".
Deleted: Graph "aaa" on "asd2".
Deleted: Trigger "bbbb

{HOST.DNS}{ITEM.LASTVALUE1} {ITEM.VALUE2} {HOST.HOST} {HOST.NAME2} {HOST.HOST3} {HOST.HOST1} {HOST.HOST4} {HOST.IP} {HOST.IP1} {HOST.IP2} {HOST.IP3} {HOST.IP4}" on "5280-2 vis, 5280".
Deleted: Trigger "a {HOST.HOST1}" on "5280".
Deleted: Trigger "a2{HOST.DNS} {ITEM.LASTVALUE1} {ITEM.VALUE2} {HOST.HOST} {HOST.NAME2} {HOST.HOST3} {HOST.HOST1} {HOST.HOST4} {HOST.IP} {HOST.IP1} {HOST.IP2} {HOST.IP3} {HOST.IP4}" on "5280-2 vis".
Deleted: Trigger "a2{HOST.HOST}{ITEM.LASTVALUE1}

{ITEM.VALUE2}

{HOST.HOST}

{HOST.NAME2}

{HOST.HOST3}

{HOST.HOST1}

{HOST.HOST4}

{HOST.IP}

{HOST.IP1}

{HOST.IP2}

{HOST.IP3}

{HOST.IP4}

" on "5280-2 vis, 5280".
Deleted: Trigger "asd

{ITEM.LASTVALUE}

" on "5280-2 vis, 5280".
Deleted: Trigger "trig 1" on "host 10".
Deleted: Trigger "trig 1" on "host 11".
Deleted: Trigger "trig 2" on "host 10".
Deleted: Trigger "a" on "host 1".
Deleted: Trigger "bt" on "host 1".
Deleted: Trigger "at" on "host 1".
Deleted: Trigger "tr" on "asd".
Deleted: Trigger "asd" on "asd".
Deleted: Trigger "asd" on "Disc host".
Deleted: Trigger "asd" on "Disc host 2".
Deleted: Trigger "asd" on "Disc host 3".
Deleted: Trigger "asd" on "Disc host 4".
Deleted: Trigger "asd" on "exp host 2".
Deleted: Trigger "tr" on "asd2".
Deleted: Trigger "asd" on "asd2".
Deleted: Trigger "bbt" on "b2".
Deleted: Trigger "asd" on "asd".
Deleted: Trigger "asd" on "asd2".
Deleted: Trigger "tr" on "5280".
Deleted: Item "aaa" on "5280".
Deleted: Item "i2" on "5280".
Deleted: Item "i1" on "5280-2 vis".
Deleted: Item "log" on "5280".
Deleted: Item "item 1" on "host 10".
Deleted: Item "item 1" on "host 11".
Deleted: Item "bi" on "host 1".
Deleted: Item "ai" on "host 1".
Deleted: Item "a" on "asd".
Deleted: Item "exp item" on "exp host".
Deleted: Item "exp rule" on "exp host".
Deleted: Item "abc" on "Disc host".
Deleted: Item "abc" on "Disc host 2".
Deleted: Item "abc" on "Disc host 3".
Deleted: Item "abc" on "Disc host 4".
Deleted: Item "exp item 2" on "exp host 2".
Deleted: Item "a" on "asd2".
Deleted: Item "bi" on "b".
Deleted: Item "bi" on "b2".
Deleted: Item "asd" on "5280".
Error in query [DELETE FROM hosts WHERE hostid IN ('10176','10177','10265','10266','10270','10271','10317','10318','10319','10323','10324','10325','10326','10327','10328','10329','10330')] [Cannot delete or update a parent row: a foreign key constraint fails (`ztom20/items`, CONSTRAINT `c_items_4` FOREIGN KEY (`interfaceid`) REFERENCES `interface` (`interfaceid`))]
SQL statement execution has failed "DELETE FROM hosts WHERE hostid IN ('10176','10177','10265','10266','10270','10271','10317','10318','10319','10323','10324','10325','10326','10327','10328','10329','10330')" [CHost.delete -> DB.delete]

I have a database dump if necessary.