I am really mad as well! Today my cat stepped on my keyboard and deleted a book.
Calibre should never have permitted it. OK, it was a terrible book and I am probably better off without it, but there is a principle involved. Both my cats are French, and everyone knows that French cats cannot speak English. So why did calibre let my cat delete a book she can't even read, hmmmm? Talk about cruddy error checking and a total lack of support! You bigots have something against French cats? Or perhaps I should say, Freedom cats?
I just can't believe that the community tolerates such a travesty. Calibre should at minimum have a paw-on-keyboard detector. Goodness, my HP-35 calculator could handle cats stepping on them, so why can't calibre? Shoddy. Simply shoddy. Calibre developers must have the IQ of a dead flashlight battery.
I must stop using calibre until this problem is fixed. Do the work, and post here when you are finished. Don't bother unless it has been fully tested. I will let you know if it meets my requirements.