Currently CfgFunctions postInit is executed before init.sqf for clients which are connected/present at mission start in MP.

[23323,201.821,0,"Executing fn_preinit.sqf"]
[23323,201.827,0,"fn_preinit.sqf processed"]
[23323,202.106,0,"Executing fn_postinit.sqf"]
[23323,202.106,0,"fn_postinit.sqf processed"]
[23328,202.395,0,"Executing init.sqf"]
[23328,202.396,0,"init.sqf processed"]

JIP clients and the dedicated server don't have the problem, execution order is correct:

[24985,254.519,0,"Executing fn_preinit.sqf"]
[24985,254.525,0,"fn_preinit.sqf processed"]
[24985,254.616,0,"Executing init.sqf"]
[24985,254.616,0,"init.sqf processed"]
[24991,255.963,0.243,"Executing fn_postinit.sqf"]
[24991,255.963,0.243,"fn_postinit.sqf processed"]

This makes using postInit quite unreliable as postInit should always run after init.sqf and never before init.sqf {F22213}