Answer:
What happened was that small particles of the syrup, presumably the larger ones (the ones with more weight), settled down to the surface of the pitcher. This would occur while the liquid inside was still. When mixing the syrup, the syrup doesn't necessarily blend into the liquid, but und up as extremely small particles, so small that you would assume that it has been completely mixed up into the liquid. However, if left still for a good amount of time, you would see some of the syrup remaining, as the weight of the particles would cause them to float down and collect onto the pitcher's surface. Again, this is possible when the liquid is still as to prevent movements on the liquid, causing the particles to take longer as the float to the bottom of the pitcher, which could be the reason why there was no extra syrup when moving the liquid from the bowl to the pitcher.