When you duplicate something by default, almost everything linked to it (IPOs, actions, materials, textures, etc, etc) get linked to the new object as well. So you have to un-link the data from the duplicated object so it doesn’t influence it anymore. To understand this better, try this little example.
-start with a new blender session, key frame the default cube’s location, advance 10 frames, move the cube and keyframe again.
-now open an IPO curve editor, you’ll notice it has keyframes and curves. In the curve editor’s header, there will be a name associated with the curves - something like objipo…or something like that, to the right of the name will be a few boxes, one will be a number (should be one) one will be an ‘F’ and one will be an ‘X’
-go back to the first frame, and duplicate the cube and move it someplace, now look at the number, instead of 1, it should now be 2. this number tells you how many users of the data block there is (or basically how many objects are using that ipo curve). If you move around in the timeline (advance or back step in frame numbers) both cubes will move exactly the same, that is because they share the same animation data (data block is blender’s terminology)
-to un-link the ipo curves from the new cube, click on the ‘X’, now move the duplicated cube someplace else and select the default cube again, you’ll notice in the ipo curve editor that now the objipo only has one user again. if you select the new cube, it will probably have no curves associated with it. Now you can create a new set of curves for the new cube (by inserting keyframes) and both cubes will now have separate animation data.
The ‘F’ button assigns a ‘fake user’ to the data. So after doing the above, if you select one of the cubes and the number by the ipo name is 1, click on the ‘F’ button and now the number will change to 2, telling you there are 2 users of this data, one is the cube, the 2nd one is a fake user. Generally, by default if you save the file and there are no users of data, it will not get saved when the file is saved. This is important because if you are working with an animation and you have created 3 actions for an armature only one can be linked to the armature at a time, and saving the file you would loose the other two actions.
Hope this helps, it’s kinda tricky while trying to learn it, but once you do, it becomes easier…