This has been a recurring issue for me. IIRC in recent couple months there were two Plasma upgrades in Debian Unstable, 5.7 and then 5.8. In both cases Plasma Discover blew away plasma-workspace and bunch of other KDE packages (including self) with zero warning. If at the very least among the list of the packages that are to be updated there was also a list of packages that are to be deleted that would already be enough to alert me. If there was also a way to prohibit the deletions and upgrade only what can be upgraded without (any major or of any manually installed packages) deletions that would be even better.
Alexey
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