When i use a command block for assign a PermissionsEx group to a player, inserting che command "pex user player group set admin", i expect to see in console "commandblock at x,y,z issued command "pex user player group set admin", but none command is logged in the console or log files.

I opened an issue with the creators of PermissionsEX (issue #2532), but they said that logging commands is a Spigot thing.