Comment 11 for bug 1489154

No, -proposed should never be enabled on a development release. We actively discourage it (it is still *possible*, but it's not done by default, and we strongly recommend people *not* to do that), because it's not abnormal for things to be broken for a period of time in -proposed during the development release. Things get updated from Debian, and stay stuck in proposed for a while because they don't build completely, cause other packages to be uninstallable, etc. Once these issues are fixed, we let them through to -release. Currently, wily is not yet released (won't be until October), so having proposed enabled can indeed break your system pretty badly -- if documentation says to enable it on a version of ubuntu in development, it's quite probably wrong and should be fixed.

This is very different from *stable* releases -- at this time, anything from Vivid and earlier. In that case, it's fine to install packages from -proposed if you want to test a fix to a bug that we're preparing an update for.

apt-get upgrade should always get you a properly upgraded system, but when -proposed is added to the mix, this can break since the packages there are "in testing", being prepared for an "official" update. Things *might* be broken.