Steps to reproduce:

1. Create a zabbix trapper item with Numeric float type.
2. Create an calculated item using upper one with Numeric float type and preprocessing with simple change type.
3. Create an another calculated item using 1. point item with Numeric float type using  change functio - change("1pointitemkey")
4. Execute the next Zabbix sender values

bash-4.3# zabbix_sender -z 127.0.0.1 -s test -k test_trap -o 20
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000171"sent: 1; skipped: 0; total: 1
bash-4.3# zabbix_sender -z 127.0.0.1 -s test -k test_trap -o 100
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000141"sent: 1; skipped: 0; total: 1
bash-4.3# zabbix_sender -z 127.0.0.1 -s test -k test_trap -o 20
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000078"sent: 1; skipped: 0; total: 1
 

Did not Calculated last check.

Expected:

-80 value would be calculated.