Starting a new neighbourhood for Seasons, I decided to have the family adopt a stray. I had never done it before, as it's a long and painful process, but now I wanted to try it.
A little girl became best friends with a cat and even got the want "Sleepy joins family". Unfortunately, kids can't adopt, so I had to repeat it all with her mother. Finally (on the last day of fourth season!), the option "Adopt" showed up. The cat was adopted by the mother, but the girl's want wasn't fulfilled. Neither Sleepy, nor the rest of family had the memories of him joining the family.
I removed all my downloads, but it didn't helped a bit. I aged the girl to teen and made her adopt the cat - again, no memories and the want remained unfulfilled. Since I've never adopted before, I don't know, maybe it's normal?
It's a new neighbourhood, with only one playable family, played for four seasons (it's 20 sim days, I think), made with empty templates. Strays were made using NPC and Townie Maker (the tree spawned by shift-clicking a Sim). I have Uni, Holiday Pack 2005, NL, Pets, Seasons and Celebration pack, but still no OFB.