Ward tells the boys in Tire Trouble it was a stupid thing to leave the garage in such a mess. Later he realizes he shouldn't have said they were stupid.

A few episodes later in Beaver's Bike Beaver says how his bike was stolen and Ward says it was a stupid and careless thing to do to lose his brand new bike. I guess Ward forgot not to call him stupid.

Doing something stupid and being stupid are two different things.

In six seasons one thing we find out about Ward is that he's quite fallible. At least, he admits it.

(totally off topic) In Beaver Runs Away and Wally's Election, he really comes clean, in very well-written dialogue.