I'm not a Debian developer. But based on my knowledge, bug fix in Debian is not tied to the upstream package.
Because the bug appear in Debian, it will be fixed in Debian. If the bug is global in nature, eg. occurs in other distro as well, then the Debian developer will forward the fix to upstream.
Thank you. I was talking about a bug in the upstream source.
So we suppose that debian developer fixes the source, uploads a new package to sid and sends the patch to the upstream developer.
In that case, since the same bug was in other distros, develpers of those other distros could send their own patches to upstream.
Upstream developer then could select the solution proposed by other distro's developer to fix de upstream version.
So when the debian developer downloads and packages a next release of the program from upstream, his patch will be lost ?
No problem with that situation ?