It's not a bug, as far as people (well, Neia! but I trust her on this) looking at code can tell it appears to me, from playing with and without and looking at what's also happening with relationship creation, to be designed to speed lot load times now that they've enabling a lot more background strong-relationship creation to vary up what you see happening around you. Sadly relationship culling didn't get fixed in today s patch. Is is a bug? Or is this what happens when Sims move?
I recently also went to one of the bars in Wittemburg and my Sim met his husband's daughter, whom he fed as a baby, helped with homework, watched grow up into an adult and move out, but who was now a complete stranger to him. During Welcome Wagon in the new house, one of the people that lived in the old house came by and her status read as just 'neighbour' and 'acquaintance'. I just had one family move from a shared household where there was another family. Question: How come Sims forget each other when they move household? Not sure if this goes in the bugs section, so please feel free to move if this is the wrong place.