The nozzle will typically leak a small amount once a print has completed, but it's barely enough to be noticeable, and usually stops within a few seconds - for longer prints (40+min) you may see leakage for a minute or so after printing has terminated. If you're seeing that the nozzle is leaking a bunch, or continues to leak for some time after printing has terminated, there are a couple possible causes:
1) Trapped air in the nozzle is the most common cause of leakage. If you recently installed the nozzle, it's common for a small air bubble to be trapped along with the ink. Small air bubbles in the nozzle usually clear within the first few prints.
2) Ink not sufficiently warmed before printing - when the ink warms up, the viscosity will decrease and it will expand a bit. These effects combined lead to increased flow rate and to some leakage if the ink was used when still cold.
3) Ink was over-primed - if you found that you were hitting the '+' a bunch to get a particularly large trace size, then you're likely to see a bit of leakage after printing finishes - if the piston applies an abnormally large amount of pressure on the ink, it will leak as it decompresses, even after the pressure has been released.