In Mathematica 10 there is a new "feature" that is rather annoying: when clicking into expressions they are sometimes selected, which is dangerous because they can be deleted. Also, in order to deselect the code one has to click again, so one has to be very careful. I guess that this arrives when the cursor is slightly glided while holding the left mouse button down, possibly along a single pixel is already enough. This is difficult to prevent because holding the mouse completely still is not easy when code is created, displaced, modified and so on. I went back to Mathematica 9 because of this but I wonder if it is not possible to disable. I tried to set dynamic highlighting on false in the code assist options but this has no effect. Also the other options in this category have no effect on this. Has someone an idea how to disable this?