Have you administered a polygraph exam? I smell a rat... a big Commie rat...
No rats were harmed in the making of this post. No offense is intended towards Communists, their families or anyone who might know or think they know a Communist. Offer void in Utah. Full offense is intended towards anyone from Utah.... just kidding.
The backups weren't created by this one-liner. -i will not create a bkup without an extension and the error's not anywhere else in your one-liner, just tested it. So see what other code is being ran on these xml files (check there creation dates versus when you run this one-liner?).
"Cogito cogito ergo cogito sum - I think that I think, therefore I think that I am." Ambrose Bierce