In stretch, lightdm invokes the user's session with SIGPIPE ignored. This can cause programs with careful error handling to fail. See, for example, #841090.
I see that this bug is still outstanding in stretch. To debian-release: The lightdm maintainers disagreed with me about the bug severity. Please would you confirm that this bug is RC. To the lightdm maintainers: I intend to NMU (to DELAYED/7) to apply the patch, unless you object. Ian. -- Ian Jackson <ijack...@chiark.greenend.org.uk> These opinions are my own. If I emailed you from an address @fyvzl.net or @evade.org.uk, that is a private address which bypasses my fierce spamfilter.