Okay, I misspoke a bit earlier. Here is a shot of my Mail app on the ipad3. This is what I get for the keyboard - without touching any keys - when the cursor is in the address field (e.g. The "To" block):
Note that the underscore is right next to the space bar. Again, this is without touching any key or typing anything. It's the default position when the app is first opened.
If your doesn't do this, then yeah, you've got a weird bug going on - because it makes no sense for two ipad3s to be different, especially given that we are both on iOS 5.1...