Spam box to INBOX

Is there any process that moves mail from an email account's spam box into the email account's INBOX? I'm trying to diagnose an "issue" where spam messages get delivered into the email account's spam box but after a period of time they get moved into the email account's INBOX. I suspect it's something the end-user is doing. Or perhaps the left hand not knowing what the right hand is doing. But I thought I'd ask.