I noticed a few days ago that my external hard drive, on which I store my Time Machine backups, only mirrors the content of my Hard Drive instead of actually backing up. I don't know if it has anything to do with that fact that I finally recently upgraded from OS Snow Leopard to OS Lion, which is the last OS upgrade my late 2007 model MacBook will accept. I'm using 10.7.5, build 11G63
I can drag files from my Time Machine backup folders going back to Feb. 22, 2013 on to my desktop, but they do not copy. Instead, they move out onto the desk top from the Time Machine folders and the same files disappear from the equivalent hard drive file folders, as if they had been dragged to the desk top. Likewise, any file I drag from any hard drive folder to the desk top disappears from the equivalent Time Machine folder. Conversely, files moved from the desk top to either a Time Machine folder or its hard drive equivalent show up in the other.
I don't know the significance of the Feb. 22 date, since I upgraded to OS Lion sometime after that.
I solved this myself. I found that, after upgrading to Mac OS Lion from Snow Leopard, some of the aliased folders in my Time Machine backup hard drive are not locked, but the regular folders are locked. Apparently this is new in Lion. (As I mentioned above, my MacBook is too old to upgrade to Mountain Lion.) I had based my query above on my ability to delete things from some aliased folders on my backup hard drive. Fortunately, they are locked in the equivalent non-aliased folders.