Yet Another Glitch Maybe?

So my sim had twins who went to high school and did all the things and when it came to graduation only one graduated even though both were there? They announced the one and then it came up saying graduation was ending soon. The one got the diploma and got the moodlet while the other didn't have anything. I just decided to move on with my challenge and have her go to university anyways. But is that something else that you guys have experienced? Like it's normal for more then one sim in a household to be in graduation at the same time.