The reason they see this is because of hidden echos...
to fix this you need to do the following...
type !menu in chat to bring up the menu>goto groups>user>manage permissions>other>then check "ulx seeanonymousechoes" this should fix it
EDIT: Looks like Bytewave has beaten me to it while i was typing... both ways should work!
Kinda.
ulx logecho = 0 prevents admin commands from being echoed at all. Setting ulx logecho to 1 shows them anonymously, and ulx logecho 2 shows the source of the command.
"ulx seeanonymousecho" permissions controls who gets to see the source of a ulx command even when they are purposely issued anonymously (ie, when ulx logecho is 1). This is intended as seconday, fine-grained echo control (ie, admins can see which op issues a gag, but users see it anonymously).
Unless you want to create a tiered approach to echoing, I would recommend ulx logecho = 2.