i personally have not witnessed it but it doens't have to have any outward signs either. i don't know what kind of dual plan your running but dual planes have the really long runners with narrow ports usually that have alot of curves. it doens't take much for fuel to fall out of suspension and create a wet wall. are you running your heat crossover or is it blocked off? really you won;t be able to identify fuel puddling runner issues unless you sample egts at each cylinder. your o2 sensor won't tell you enough.

advancing the timing and running a cam with less overlap will help with the reversion as well.