Well, as one of those upstream authors whose code was patched: I was never contacted about it, so I never knew there was a requirement to be met, and so they carried around a bad patch for years, about which I knew nothing. Once a user pointed this out to me, the next release fixed the underlying issue in a better way. After years in which the Debian folks didn't file an issue or report the problem in any way that I could tell.
Mind you, Debian is not alone in this, it happens with other distros, too.
And to be fair, I think this rather depends a lot on the downstream package maintainer; I've witnessed this with other projects where they were quite good in interacting with upstream to get something sorted out. I am not really sure if any policy Debian/Fedora/... could enact would really help with it; people can (accidentally or intentionally) ignore them.