See the marker on the left hand side of the visible item -- that is the loop end marker. The item actually starts way off the the left somewhere. What happened is that you had an item looped several times, then trimmed the left hand side so that you are looking at loop number X, and the loop length itself does not fall on the grid that you want to quantize. You are quantizing the first loop, not the loop you are looking at. If you extend the left hand side so that you get back to the start of the actual item, you will see that it is quantized. Imagine that you were looking at two loop cycles, and the loop length did not fall on the grid. What would you want to happen when you quantize?