I've seen it. We had a BMX bike come into the co-op once that the owner had converted to left-hand drive by simply swapping the cranks over (obviously he had a left-hand drive rear wheel too). One pedal (I forget which) had worked itself loose. The shoulder on the pedal spindle was about a turn away from the crank face, and he hadn't ridden it very far. We tightened whichever one it was up, but while I wasn't there he apparently brought the bike back again with the same problem.