Graphic Bugs CAN Be Fun!
I saw that happen once with seven sims. I made a mother with six child daughters. They spent the first half day of their lives in their new home meshing with each other on the front walk until one by one they separated and went about their business. I had a video of it, but I've deleted it now.
No, wait, I still have it! I hope I do this right. Yay, I did. If you click it you can watch the video on Photobucket. I guess the sixth daughter was a toddler and not involved. The mother was involved, but she's in a completely separate minute-long video, so I thought I'd just post the one.