Hi. This is a summary of all I know about the problem:
Apparently, it started to happen when using sbuild 0.89.0, which was uploaded for unstable this week. It seems to happen only when using schroot. Admittedly not the default anymore in the buildds, but still a way in which anybody might want to build packages for whatever reason [*]. Several days ago, I did a full archive rebuild using the unshare backend to make sure that sbuild 0.89.0 was ok for release. This explains that I did not find the bug before, but it's now that I tried again using schroot (not the unshare backend) when we discovered the problem. I've asked sbuild maintainers about this in case it might be a regression in sbuild, but maybe sbuild is just being a little bit more strict (for good) in what it allows the package to do. [*] There is some similarity between this bug and packages trying to access Internet during build. Not all sbuild backends will catch packages trying to access Internet, and not all sbuild backends will error when the package tries to write to $HOME. This is why I'm still using schroot while Lucas Nussbaum has switched to the unshare backend. I agree with Jeremy that this is worse than breaking reproducible-builds, for the reasons he stated. In either case, I've given Mathias a VM where at least he can verify that the package writes to $HOME (with or without a build failure, I still don't know why there is a difference here), and he says he has a potential fix, so hopefully we will have a package which works for everybody. Thanks.
