Personal lists showing as modified without me making any changes

I've noticed this two or three times in the last month or so. I view my lists, or I click on the drop-down menu beside the "Add to Watchlist" button on a film's page, and the most recently updated lists are different from what I know I've edited myself (usually by adding a film to such a list). Based on the most recent occurrence, where 7 of my lists show as being updated yesterday despite not adding any films to them, I suspected that a film was removed from the database, or perhaps merged into another title.

I downloaded the shortest of the affected lists and looked for any films modified yesterday, and discovered that Supernova (2020) was merged or reassigned a new ttid (the old one was tt11169050), and it's on all 7 affected lists. Is this new behaviour after recent updates, or have things always been like this and I've simply never noticed?

It's confusing, because I didn't make any changes, rather they were backend changes to the database, so the "last modified" doesn't accurately represent when I last modified the list, but when something on the list was changed by IMDb.

Thanks.