Misshelving is the only rational explanation

"I rented the other day..."
While she paused to think, I wanted to tell her to stop right there, that this couldn't end well, that no conversation I've ever had has been entirely pleasant if the other party thinks s/he 'rents' from the library.
"Um..." she hesitated again. "Four tapes of Roots, I rented four tapes of Roots, 'cause you know you can only rent four at a time, ya know?"
"Yes." I considered how best to ask her what her question was as I waited to see if she would actually ask it.
"Well, and there are more than four tapes, and I want to watch the rest, but I can't find 'em."
"Oh," I brightened up. This should be easy. "Okay, they'll be... well, they would be right here if they were in, but it looks like the entire series is checked out."
"No," she said, shaking her head slowly, maintaining eye contact. "I checked out the first four."
"Right..." Again, what is she asking? "Somebody else has checked out the rest of them."
"No," she repeated. "I had the first four, and I just returned them. Just now."
"Yes, so somebody else must have checked out the last ones while you had the first ones."
"No," she insisted again. "That would mean they watched the last ones without seeing the first ones. That'd be out of order. They must be in the wrong spot."
"..." Though an ellipsis can't be verbalized, I'm fairly certain I stood silent for at least a second or two with my mouth open. "Maybe they checked out the first ones before you did."
"..." Her mouth was mostly closed during her ellipsis, her jaw jutted to one side and her brow furrowed. "Oh. Yeah, I guess so."