How can I keep my sims from being sad about their birthday?
I usually play on unlimited lifespan instead of auto-aging, but I'm doing a challenge right now that requires a normal lifespan. I throw my sims a birthday party when it tells me to ("Celebrate [Sim Name]'s birthday by throwing a rocking Birthday Party!"). People come over, I get a gold level achievement for the event, the birthday sim blows out the candles and....doesn't age up. Then the next day, they age up and cry all day because their birthday was forgotten. What?! Am I supposed to wait until the day after I'm told to throw the party? What am I doing wrong??? It's really annoying having them mope around after I JUST threw them the greatest party of all time, so I would really like to know how this mechanism works. Thanks in advance.
(Edit to add: I should note that my current generation had twins. One aged up normally at the teen --> young adult birthday party and one did not, even though they both blew out candles. I haven't been able to throw a successful age-up party since and they are both now adults. I don't know if this is a bug or if I'm doing something wrong. I am assuming it's not a bug until I'm told otherwise.)