Hmm, as a Linux from Scratch (and Beyond-*) user and editor, I've often broken my builds when updating. Occasionally,I even have to use multiple-version workarounds (currently, older ffmpeg for transcode, which we've now dropped, and gst-ffmpeg [ yes, I know that gst-ffmpeg devs dislike using system ffmpeg, but their version of ffmpeg was *so* old last time I looked).
I've also seen problems in specific packages (e.g. abiword with some past versions of libxml2). So, I expect that from time to time there will be *some* breakage on my desktop. But, that's "my system, my rules, my breakage."
I don't expect my changes in the books to break functionality - if they do, I try to fix the problem. I had assumed that all distros took a similar "we don't deliberately break it, but if it's broken we will try to fix it" attitude. Sounds as if I'm too much of an optimist.