Yeah, I noticed that too. I thought mine were broken at first. It turns out that that it just takes a good bit longer between when you press the power button until it actually powers on if it's plugged in. If it's been plugged in for a while on the battery screen, then pressing the power button makes it come on immediately like normal. The delay happens if you either plug it in and immediately try to turn it on, or if it's plugged in, turn it off, and then immediately try to turn it back on again when the battery display comes up. Weird.