kerneltask taking all cpu when using external monitor only since 1.8.1

Hello everyone,

I've got a Macbook Air (Late 2010).

I've got a "kerneltasks" suddenly taking all cpu on such conditions

- using an external monitor + keyboard + mouse/trackpad

- only when laptop is closed

- it can take a few minutes up to an hour or so before getting high on CPU

- it goes back to a regular behaviour when I open the laptop again (monitor still closed), but the problem usually comes back

- it happens only since 1.8.1 update

- it's a prior process so the whole mac is lagging

- momory, disk, and network usage stays regular all along, before, during, and after the kerneltask burn out

So now every hour or so, I open my laptop and close it again when it starts to lag

Anyone seen that already ?