I noticed that the touchscreen on my iPhone 4 does not register any touches when I reboot it while it is charging. It calls up the passcode lock number pad and shows only a carrier name in the upper left without the bars/wifi-3G symbols. This is a reproducible error. It disappears if I unplug the phone and then reboot it.
I have SBSettings, Backgrounder, and FakeCarrier installed through Cydia.