Given that Debian's standard installers have always been pretty bad at configuring any non-trivial disk set-up without manual intervention, I feel some people here are a little too quick to criticise. As I said in another post, I don't know why the systems where that issue came up were originally set up as they were, but there have certainly been times, particularly before the current generation of bootloaders, when that sort of set-up wasn't unusual.
The point remains that this doesn't matter. Before the upgrade, there was a fully working system. After the automated part of the upgrade, there wasn't. The original question was how safe the upgrade from 7 to 8 is, and this is a demonstration of the fact that such upgrades can carry risk. I'm not saying don't do them, I'm not expecting Debian maintainers to be omniscient, and I'm not telling you your child isn't beautiful. I'm just saying if you're thinking about moving from 7 to 8, be aware of the potential that there will be things the automated tools can't or won't do for you that may break your system, and plan your upgrade or other migration strategy accordingly.
No one argues the packaging system can handle every possible situation. It's just that this case seems, on the face of it and without knowing any of the details, have been one where the system was manually placed in a state where the updater was broken.
I'm not a DD and I have no vested interest in it, but that particular data point is an outlier no matter how you look at it.
There are more obvious situations where updates will break your system. Most common probably when you've installed third party packages with dependencies on system software. But that's not generally what's referred to when asked if the update process is stable. Such things will break no matter how stable the process in itself is.
The point remains that this doesn't matter. Before the upgrade, there was a fully working system. After the automated part of the upgrade, there wasn't. The original question was how safe the upgrade from 7 to 8 is, and this is a demonstration of the fact that such upgrades can carry risk. I'm not saying don't do them, I'm not expecting Debian maintainers to be omniscient, and I'm not telling you your child isn't beautiful. I'm just saying if you're thinking about moving from 7 to 8, be aware of the potential that there will be things the automated tools can't or won't do for you that may break your system, and plan your upgrade or other migration strategy accordingly.