I only got the zero level problem when I used the 'RGBgenie Micro Zigbee Dimmer' driver, it has never happened since. My guess though is that I have made a mistake while using that driver simply because you have had good success (after your initial problem).
Although I cannot say for certain as I have no basis in fact, I beleive that when digital off was used, it set the level to 0 and when digital on was used it restored to the original level. This means that once set to level 0, physically turning the switch on starts at that value.
I just installed another of the same switches over the weekend and had exactly the same experience as before (both zero level issue and not reporting physical changes to the level). I have no idea why, I thought it may work like it has for you. As I said, perhaps I am setting it up wrong or somesuch. I might trying flipping the driver back and seeing if the problems persists and see if I can figure out why.