Title says it all really -

when my N9 is charging, the screen becomes very unresponsive. It won't register my finger swipes, or touches, or does so jerkily, resulting in very unpredictable behaviour - screen not changing, for example, or an application opening instead of moving from one screen to another, or just nothing happens at all. Zooming in and out, or selecting an icon to move on the app screen, is almost impossible, as everything just jumps around.

At the same time, the Swype keyboard is unusable, the line is full of jaggies and missing bits and little shoots that go off sideways. I just get random letters.

And the little charging indicator at the top, instead of filling smoothly up to the top and reverting back to the bottom, jerks up and down really fast and in an unsteady way.

Meanwhile, I can't unlock the phone by double-tapping on the screen - nothing happens. I have to press the power button to unlock. Luckily I have it set to get past the lock screen with a double press, because otherwise I would be stuck on that screen, unable to get rid of the wallpaper.

I've checked CPU while it is behaving like this and see nothing unusual. It only seems to occur while it is charging. And once the battery is charged (or I unplug the adapter) the phone becomes normal again. And sometimes it is normal while charging - though not often.

Anyone seen behaviour like this?

Change your charger.

There was some big thread about this well-known issue, and a bug has been raised, but I just can't seem to find it...

Is it the wrong voltage? I use more than one charger.. don't think there is a difference between them.

I have the same issue with the N9 charger.
The old N810 charger together with a micro USB adaptor OTOH works fine.

OK, so using a non-Nokia adapter appears to be the problem... switched to the standard supplied Nokia one and no issues. Though the little charging icon is still zipping up and down like crazy.

What's happens if you charge it via USB port?

AFAIK using most chargers results in this problem. I've read somewhere that the current interferes with the capacitative screen hence this problem.

Hope Nokia manage to get a fix of this but i think due to the hardware design its not going to be an easy fix.

I do not have this problem at all.

No issues with my N9s too... I've made calls while charging... all smooth & perfect.