I only had time to read this rather quickly, so I can't make any kind of intelligent remarks on it. But it is fascinating, mainly because I don't realize that such an "interference" could occur. I don't recall making that type of mistakes when I was an undergraduate, and I'm not claiming that I'm smart either!
The study looked at how students learning electrostatic and magnetostatics answered questions on electric field force and magnetic field force acting on a charge particle. You'd be surprised that the understanding is non-commutative!
Abstract: We investigate student confusion of concepts of electric and magnetic force. At various times during a traditional university-level course, we administered a series of simple questions about the direction of force on a charged particle moving through either an electric or a magnetic field. We find that after electric force instruction but before magnetic force instruction most students answer electric force questions correctly, and we replicate well-known results that many students incorrectly answer that magnetic forces are in the same direction as the magnetic field. After magnetic force instruction, most students answer magnetic force questions correctly, but surprisingly many students incorrectly answer that electric forces are perpendicular to electric fields, as would happen if a student confused electric forces with magnetic forces. As a further indication of interference between electric and magnetic concepts, we also find that students’ responses depend on whether electric or magnetic force questions are posed first, and this effect depends on whether electric or magnetic force was most recently taught.
It's astonishing that some students can get that confused. I have to read the paper closer to see if they came up with a rational reason why it occurred.
If any of you teach intro E&M, do you see the same thing in your class?
 T.M. Scaife and A.F. Heckler, Phys. Rev. ST Physics Ed. Research v.7, p.010104 (2011). You may obtain the paper for free here.