Right i've just experienced the double character annoyance for the first time and this is after 5 days of use. What i found to be causing my problem was having the power supply connected whilst it was fully charged. I'm sure i've used it like this before with no probs but can't be 100% sure.
Same here. Up till now have used the vega unplugged. As soon as I plugged it in last night the double characters and over sensitive response started immediately. I unplugged it, it stopped, plugged it in, and it started again. the battery was not fully charged either.
I think having the mains adapter attached affects the capacitive nature of the screen. I must also say I think the mains charger is extremely shoddy and there has been a report on another thread of a mains adapter blowing completely.
Please report any issues you experience and we can report back to DSG. Personally I wouldn't trust this mains adapter. Recently I had a laptop with a cheap replacement mains adapter that was clearly not good. Every time you touched the laptop lid when plugged in you could feel a vibration/discharge - really weird.