There's a minimum time for executing a note. I haven't measured it with any precision but I've noticed that at a tempo of 1/4 = 100, 1/16 can cause delays in the next note. 1/8 is usually fine. At 1/4 = 120 or faster, 1/16 will almost certainly be out of time.

If you want to record passages with brighter tempos, you might have to split the melody between two tracks to avoid dragging when there are 16ths.