Blender Version: 2.69 official (win 64)
How to Reproduce: Select last Z-location keyframe in graph editor. Press G > X and notice how, during transform, the entire keyframe, along with its handles, snaps to each frame by default. That's the expected behavior. Next, press Shift+D > X and note that while the keyframes snap to each frame, the handles do not.
This is a very minor little bug, but it can lead to precision issues when duplicating keyframes repeatedly. With each iteration, the handles get skewed, requiring the animator to correct the handles.