Vector to shapelayer - editing weird thing

Hi,

I have an ai-file where I can created a shapelayer from a vector layer.
I have done that before. I works fine.

But now when editing with the pen tool, when I try to move the point in the path the point jumps away on the screen.

When I use the convert tool it works fine but not the pen tool.

Any idea what that could be? I use a wacom tablet for editing.