proc.num[<process>] return zero for some working processes.

Strange situation with monitoring of MS IIS AppPool:
item
proc_info[w3wp.exe,all,<any param>]
returns the result differ to zero , but
item
proc.num[w3wp.exe]
always returns zero.

for some other processes proc.num[] returns not zero result.

This reproduced on win zabbix agent ver. 2.4.4 and 2.4.5
Zabbix agent runs from localSystem account or account with administrative rights.