We seem to have a few issues here. First, with the heat being too high in the beginning, and then reducing it, some time must be given for the column to regain equilibrium after the decrease in heat. Although it sounds like you gave ample time ,16 oz., for this, the proof that you report does not support this. You want to be sure that you have a stable temperature showing on your thermometer, no surging, and only a fast drip coming from your condenser. A distillation rate of 12-15ml per minute is usually pretty good if you want to obtain high purity. Also, if you split a small volume of product, then the accuracy in getting an exact 50:50 ratio is difficult. I would also guess that if it etched your plastic test cylinder, that the abv was above 40%. If the proof that you report is correct, I would guess that the distillation speed must have been much to high.

Usually the cause of distillate going cloudy with the addition of water is that of minerals that are soluble in water and not soluble in alcohol. When the minerals are introduced to alcohol, they come out of solution and make the liquid cloudy. The fact that this only happened with your first sample, but not subsequent samples leads me to believe that just the opposite happened- that there was something picked up with the first part of the run ,from cleaning the equipment, etc., that is soluble in alcohol but not in water, and when the water was introduced this came out of solution to cloud the distillate. This is a 'best-guess' based on the information that you have given.