Here's instance #2 for ya Jay.

A Dakota on our field was owned by a VFR only pilot. Last summer on a trip
from STE to GRB and back, he reported having carb ice 3 times during his
trip. He questioned that it was really carb ice, but said that each time
the engine started to sputter, carb heat smoothed out the roughness in text
book fashion. Each time, the engine then ran smoothly for awhile then got
gradually rougher until carb heat was applied again.

I was at the airport when he returned and reported the problem to the
mechanic. To satisfy the pilot, the mechanic looked over the airplane and
found nothing wrong. It was simply the effect of a very humid day.

Jim