I've had that problem too. I think it all depends on when you last visited them. yoyo and I now believe it's a 10 hour or 12 hour gap between them as you can sometimes visit them twice in one day for credits, but not always.
That happens constantly with my computer while I'm either the Haunted Mansion Attic or Haunted Mansion (wherever Phineas is). Mostly with where Phineas is. But I click on him, everywhere to tell you exactly, and it doesn't give me credits completely. I hate that.