I was building up a motion track using puppeteering, layer by layer, which works fine: everything that's added gets combined.  I added eye-blinking to the facial layer, which worked fine: eyes are blinking properly. Now I add an other facial animation. After that my quickly blinking eyes have suddenly slowed down. So apparently the facial animations do not properly add up.  I did a little test and when the blinking happens when there is no other facial animations; things are fine.