Each time calling wmi.get, the zabbix agentd process leaks memory. After a while this memory leak grows into hundreds of megabytes. Seeing zabbix agentd processes hanging around using up to 800 MB of RAM is not uncommon.
To verify this, I've written a powershell script that repeatedly calls wmi.get 4 times (see attachment zabbix-memory.ps1). After 100 iterations of this, memory usage of the agentd process has increased by almost 1 MB (Start: 7392, end: 8288 kb, delta: 896 kb).