Why would you have to warn a staff member? If it's one thing, they created the rules, not us. They also have to follow the rules just like we do. They also have more expectations as staff (very little to no room for error in their behavior). They had their warning already by reading the rules, filling out the application, and then enforcing the same rules. No additional warning is required if a staff member breaks a rule.
Believe it or not, there actually is a rule against swearing in the voice channels. A mod said this himself.
If its accidentally.. I know, staff should't be so careless and should pay more attention around here. I agree with what you said above.