Hey guys,
I think I may have a similar issue. There is a definite delay when I tap the back button, to the point the key could be described as unresponsive. However, my problem is not consistent and can happen sporadically. It tends not to happen in mid use but when I haven't done anything for 20-30 seconds it can take 3-4 repeated presses before it responds/wakes up.
It's not a major issue but can be a bit annoying.
Thanks for your help!