When I turn on the lights in my car, the player dims immediately. However, when switching them off, the player takes a couple of seconds to react. Why would the dimmer need a different time to witch itself on, than off????
This bothered us too when we first implemented that feature. The answer is, that many cars don't just switch the lights on and off in one go: they fade between. Moreover, they don't fade by smoothly ramping the voltage from 0 to 12V: they start with a few narrow spikes of 12V, then make the spikes wider and wider, until eventually the spikes "merge" and it stays at 12V.
For an analogue component like a lamp, this is an absolutely fine way to behave (the switching is very fast). For a digital component trying to sample the line, it's a complete nightmare.
We fixed the problem by making the empeg wait for the line to be stable for a while -- so we can distinguish the line "really" going up or down, from the line being "flickered" up and down. This does involve a short delay, though, which you've noticed.
Peter