We've had users reporting that their email white and blacklists have "disappeared." Upon further investigation, their Usermin module shows no addresses listed in the "From: addresses to never classify as spam" and "From: addresses to always classify as spam" boxes, yet their ~/.spamassassin/user_prefs files are filled with whitelist_from and blacklist_from entries.
With a test user, this is reproduceable by using Usermin to add an entry to "From: addresses to never classify as spam" - the address gets added correctly to the user_prefs file, but when the webpage reloads after the submission, the box is still blank.
As the module is used only occasionally, I cannot be sure when this started but our best guess puts it in mid to late November, likely coinciding with the Usermin 1.310 release.