One of the few commanders who were successful in Iraq in that first year of the occupation, Lt. Gen. David Petraeus, made studying counterinsurgency a requirement at the Army's Command and General Staff College at Fort Leavenworth, where mid-career officers are trained.
"One commander 'was' successful, not one commander 'were' successful," the reader observes, and it's hard to argue with that. But the sentence wasn't saying that only one commander was successful; it was saying that few commanders were successful and that this commander was one of them. To put it another way, the sentence wasn't saying that he (a) was one of the few commanders and (b) was successful; it was saying that he was one of the few commanders-who-were-successful. One of the few successful commanders, not one of the few successful commander.
This sort of construction would be my top choice for bait to dangle in the hope of fishing dilettantes out of a pool of sticklers. Any others come to mind?