The one I can think of is if they subscribed to a bunch of feeds that don’t include the articles and then enable something like readability or af_comics.
i think this (rehash on active plugin list change) is one of those things that might go here or there, arguments might be made for both ways to behave.
if i was implementing this now, i might have chosen differently, but since this how this has already worked for years and the only arguably strange synergy is with the redheaded stepchild option (mark unread on update) i’m not sure if its worth it to suddenly change it.
also, remember that changing this would ALSO rehash everything AGAIN. 
@JustAMacUser and @ovalwonder I think those are valid points, too, sure. The thing is that “Mark unread on update”, be it the “redheaded stepchild” 
or not, is imho a great feature to keep track of changes in blog (and forum) posts, so you won’t miss the latest edit.
I agree that this would be tailored more to the way I look at it and how I’m trying to use this feature, but I still have trouble thinking of a use case where the end user would like to have almost all its articles, dating back years and years, marked unread, because they tried en-/disabling a certain plugin.
Ah, I’m thinking I might be able to “hack it” to my personal needs in my updater script. First gotta find it in the code, though… 
Wait! What!? You don’t purge articles?
Hehe fair point! Got some really old articles starred/published, though. Plus, when following topics, the amount of articles that are marked unread goes well beyond a 1000 at times.
https://git.tt-rss.org/fox/tt-rss/src/master/classes/rssutils.php#L19
see, it joins calculated value with the list of loaded plugins. you can replace that with sha1($tmp) etc
Thx for pointing this out! I’ve added it to my little script, all good now 
Is it possible that changing the hash calculations causes the following problem by any chance?
Since doing so, I regularly see that “Fresh articles” does not list all articles that fit the criterium. For instance, an unread article that is only an hour old is not listed among the Fresh articles, but the Fresh articles count in the navigation bar does include that article (e.g. the count is 2, but only 1 article header is shown).
E: the unshown item can be from a feed that has other items that are shown in Fresh articles.
I just updated to the latest commit and changed the rssutils.php line 19 return sha1($tmp); again (before replacing the files), just like it was before this update. Now, I’m again stuck with thousands of articles that are marked unread again for no reason…
why are you doing this to yourself? 
The simple reason is that I want to know if someone edits their blog post or changes their comment in a topic. This happens all the time and and is always contributive to the topic, and I would miss the updated info if I didn’t set the “mark unread on updated” to true.
That’s a very good reason for trying to use it, I’d say
But I’ve found now that the new $enclosures has caused the hash recalculations…