As soon as I logged in to a 19w41a version world, I saw and heard some paintings drop off walls. They seem to drop a few seconds after logging in, or teleporting back from the Nether. If I replace a painting that didn't drop, the newly replaced ones will drop in subsequent logins.

Also, for some reason I can overlap paintings in a corner, but if one were to be replaced, it wouldn't be possible, but the painting will drop after login.

Note, this behavior never happened before, but I've placed all my paintings tightly next to each other in a small house.