Steps to reproduce:
Create SNMP walk item for oid which returns units
Example: walk[1.3.6.1.2.1.25.2.3.1.4.1]
Press Test: .1.3.6.1.2.1.25.2.3.1.4.1 = INTEGER: 1024 Bytes

Remove MIB file which is responsible for this OID (HOST-RESOURCES-MIB) and restart Zabbix server

Press Test: .1.3.6.1.2.1.25.2.3.1.4.1 = INTEGER: 1024

Expected:
walk[*] item returns consistent values independently of any MIB files.
Only raw values are returned and units are added later in Zabbix item configuration.

walk[*] output is equal to output of snmpget with flag -OnU