One annoying aspect of using CATIA is when you attempt to click one of the little plus signs in your specification tree but you miss and accidentally click a branch instead. Your models goes a shade darker and when you try and zoom in on your model it instead makes the tree get enormous or extremely tiny. To turn this option off simply go to Tools>Options>General>Display>Tree Manipulation. Disable the tree manipulation option by unchecking the box. Now this will prevent unnecessary tree zooming. If you still need to zoom in or out on the tree in this mode hold Ctrl while scrolling the mouse wheel instead.