I don't think I held to any "common misconception" listed until I got to this one:
Lemmings do not engage in suicidal dives off cliffs when migrating. This misconception is due largely to the Disney film White Wilderness, which shot many of the migration scenes on a large turntable in a studio. Photographers later pushed the lemmings off a cliff using a broom.Thanks to J.S. for the link.