I'm not sure what's happening with this (is there any rough timeline??), but as others have noted, this is causing serious confusion among users, and has the very real potential to increase the risk of causing corruption, due to users refusing to perform a 'mysterious' and 'dangerous-sounding' operation to "purge" their "deleted" items from "disk".
I must say, that this is not only for the general public. I myself am wary of this, and I do have reasonable computer programming knowledge — I have contributed code for application development before (unrelated to TB), although I would never claim to be a "software programmer" per se. Sure, I can understand the (purportedly) intended meaning after it's explained on the forums (e.g. https://support.mozilla.org/en-US/questions/1308222 ). But without that, I would say the meaning was ambiguous at best.
Another point that made me very worried was that the compaction size jumped up suddenly.
Come to think of it, I don't think I received the old (or new) "compaction" message for quite some time.
I used to regularly see it every week or two, and the size of disk space to be saved was typically in the range of 20 to 30 MB, because I had specified "Compact all folders when it will save over 20 MB in total" in the general Options.
The recent/new message I got was:
The messages you have deleted can be purged from disk. This operation will save about 235 MB of disk space. Select the option below to let Thunderbird do this automatically without asking you.
[tickbox] Remove message deletions automatically and do not ask me.
Emphasis added. The problematic words are in italic. More on that later. But the big concern I mentioned was that suddenly the amount of space that could be saved had jumped to ten times larger than what I was used to. Naturally this gave the impression that rather than (only) compacting folders, a much more extensive set of "purge" actions would be activated if I assented!
I have just now reviewed my settings in the general Options, and now they say "Compact all folders when it will save over 200 MB in total". I cannot at all remember changing this, and I therefore ask the question — during one of the recent updates, perhaps connected to the present bug, was a related new bug introduced whereby user's extant settings regarding the compaction threshold were ignored and overwritten with a universal default of 200 MB??
This is a query, because I have no way to go back in time and check whether I changed the setting despite having no recollection of it, but I wonder whether it's happened to anyone else? I imagine this is something that could be checked. Sorry if I should report it on another thread, but it seems strongly related to me.
My system: TB 78.7.1 (32 bit) running on Windows 8.1 (64 bit), on the "release" update channel.
OK, back to the wording of the message. There were two more words that I have highlighted above that were not emphasised by other correspondents:
"from disk" makes it sound like messages will be wiped forever, and this is mainly problematic because users don't ordinarily think (at first) of the messages being on disk, but rather in folders; can this be changed to something to do with folders?
"*automatically" does not make it clear that the action will be only taken after a threshold is reached; therefore I suggest either replacing this with "regularly without asking me" or "automatically when the specified threshold is reached (do not ask me)"
Rather than overcomplicating the discussion, I would also be happy to just go back to the old wording that (almost?) everybody seemed to be happy with.