What causes this?

[brefos77]

Have you ever noticed the last A in America sometimes has a "curved" looking line in the middle, while sometimes it's straight? Even the bottom corners are different.
Is it post mint, or a very minor die break? I see it all the time on different cents so I'm sure it's no variant or anything.

Here's two 1989 P cents. Check out the A's:

http://i60.photobucket.com/albums/h17/brefos77/1989a2.jpg

http://i60.photobucket.com/albums/h17/brefos77/1989a1.jpg

[Steven]

I would have to say die deterioration. But that is just my best guess from what I can see.

Steven