I can't remember the last time I heard this word used correctly. No, when "misnomer" goes out in public nowadays, it's taking the place of "misconception" or "misapprehension." Though wearing a disguise, "misnomer," in perfect irony, acts out its true identity—a misnomer is a wrong name.
Here's the difference between "misnomer" and "misconception": It is a misconception (a wrong idea) that sitting in a draft will cause one to catch a cold. The "American Civil War" is a misnomer—the bloody conflict was far from "civil."