Alt-D henceforth

I have two objects that I have duplicated. The first object and it’s duplicate seem to be completely separate. What I do to one, does not affect the other … just as I would expect.

The second object and it’s duplicate seem to be acting together. If I extrude one, the other follows. If I animate one, the other jumps to the same position as the other and both animate as one.

I don’t see them grouped nor are they parented. I simply did Alt-D on both objects then started to change both duplicates. What’s bugging me is that the first object is just fine, the second is driving me nuts.

Why is the second object and it’s duplicate acting as if they are one?

alt+D duplicates and links, try using shift+D

moffboffjoe is correct. but a more in-depth answer would be:

Alt+D copies your object but uses the same mesh data. so you could have a bunch of objects all using the same mesh data, then when you change one they all change.

Shift+D Copies your object but it also makes another set of mesh data linked to the new object. then when you change one the other mesh is untouched.

there is a great tutorial video at Blenderunderground about how Blender currently uses data. (im not sure if any of this will be the same in 2.5… but for the time being the info in the video should be roughly accurate)

http://blenderunderground.com/2007/09/09/blender-basics-part-4-released/

that is the 4th video in the series. all are worth a watch. (the part most relevant to your question starts around 26:00 in that video and the alt+D info is at 39:00)

hope that helps explain why that was happening

I will shift-D! Thanks.