Maybe not intentionally, but given IT's "consistency" of experiences, it often seems so. They have algorithms that adjust pricing based on length of stay and how close the date is, so I wouldn't doubt that availability gets thrown in too, especially with the screwiness of the orphan room "logic". It may not be so much altering of the price, but altering what they are willing to show you as available. For weekend trips where I just needed a 2 night (fri & sat), or just 1 night (sat), the pricing I see on Monday is usually different than what I see on Friday, for the exact same room category. There are times when it will refuse to let me book a single night in a standard room until Friday morning. I'm sure that every time this has happened to me, it was just magical timing that someone else canceled a reservation at the last minute. Of course not, it's the orphan room. It has happened often enough that I am more than comfortable getting in the car Thursday evening to drive that direction, because I KNOW something will open up and I can book something before we drive under the gates. I wouldn't be surprised if their orphan room logic has actually created MORE orphan rooms. Granted, nowadays, I prefer to stay offsite anyway. There have been times when the price dropped $50 from Thursday to Friday. Earlier this year, I saw Boardwalk drop to under $200/nt for a Friday and Saturday night (which are the two expensive nights of the week). That was over a $100/nt drop overnight. Same room category, same view, no discount, etc. I'm sure in their system it might have been labeled a "last minute discount rate", but as far as the website was concerned, it was a standard rate that was altered because of lack of demand (the hotel WAS pretty empty), and they'd rather let it go cheaper than have it go empty.Disney doesn't have resort pricing that alters based on demand.
If you are booking 6+ months out, you wouldn't necessarily notice some of these quirks (I am almost always a last minute minimalist planner), but I have seen where 6+ months out rates are higher on weekends that have things planned (marathon weekends, as an example) than the weekend prior or after, even tho all those weekends are in a non-peak season and SHOULD be the same rates. I always check the "standard" rates first before logging in to see possible discounts, because I've actually seen the "discounts" give me higher rates. Same room same line ... should have taken a screen shot the time I saw the worst example of it. First price on the line, the "standard" rate, was the lowest of the 3, the "sun and fun" or something similarly named discount was $20/nt higher, and then the AP rate was another $20/nt higher than that!
As for the original poster, if you haven't already called to see if they can correct, try a new ressie with your preferred dates from a fresh browser without any cookie crumbs to see if it's truly available at the reduced price you'd expect. One of the cute little IT "features" that I've run into is that after you start a package, put it in your cart, then play around with the dates or room component, the "package" can become unhooked. You can get all the components, but the system doesn't see it as a package. That happened to me on a DLR reservation with tickets. I had utilized a Disney Visa link that was to get me some goodies if I booked a package. I booked the hotel and tickets together, but because I played around with the dates a little to get the best room price (Grand Californian was within $30/nt of the other two on the two nights I ended up with), the "package" status disappeared. They told me when I got there that even tho I had a room AND tickets, I didn't have a package so I didn't get the goodies. I had them go to the website, start a package, change the dates, and see what happens. They gave me my goodies. It sounds like that is what the system is doing to you when you drop the one night. The package deal link is going away, when it shouldn't. It's not that it isn't truly available, it's just one of those IT "features" making it disappear on you.