brakes pad failure mode?

[glen powell <gpowell@acacianet.com>]

When I replaced the front brake pads in the 4KQ race car I found that all
four pads separated from the pad backing plates. This seems like it
might be a rather nasty failure mode on the street or track...(!)
 The car had hibernated for > 1 year outside with no use and the backing
plates were somewhat rusty, but were new only months before the
car went into hibernation.

Is this failure mode common or rare? Thoughts?

Thanks,

-glen