I am using Illustrator CS5. As I completed portions of a complex drawing, I grouped the completed objects then locked and hid the group while I worked on other sections. Later, when applying Divide Objects Below in the same layer, the objects in the LOCKED and HIDDEN group are also cut (or "divided") if they were below the "cutting" object.
Is this supposed to happen? It is very repeatable: create a new layer. Draw some rectangles with no stroke (just fill). Select them, then control-G to group, then lock the group and hide it using the Layers panel (there is no "eyeball" but there is a padlock). Now draw then select another shape, say a rectangle that overlaps where the other objects are (even though you can't see them). Click Object->Path->Divide Objects Below. Show then unlock the hidden group and voila! the rectangles were cut by the operation.
Either I don't understand what Locking and Hiding is supposed to do, or there is a bug in Illustrator, or someone thinks this is an intuitive way for the operator to behave.