You can disable it by going to Tools > Options... > Keyboard and Mouse > Key Bindings, then searching for the command "mou-click-copy", and removing it's key binding (Ctrl+LButtonDn)
I have to do this when I'm working on a laptop keyboard, where it is all too easy for the palm of your hand to brush the touchpad at the same time as hitting the Control key.
I agree there probably should be an option for disabling this, because removing the key binding is not intuitive.