I'm well aware of them doing that ahead of a 4/$10 and other like promos. All I was saying is that changes like this mid-way through a sale may actually be the result of another factor.
They do - when there's about to be a sale. It's why they bump up the price of most sub-4.99 games right before a 4/10, or when they had the multi-leveled 4/10; 4/40 deal going months ago, they raised the price of every single game in between the ranges so that it seemed like a better deal. And then in the weeks that follow a specific type of sale, they slowly drop the prices back down of most of the games they'd just raised. It's not terribly complicated, it's just meant to provide the illusion of a discount while keeping games mostly the same price.
They do always miss some, though, and then, combined with ridiculous glitches, tend to be where the deals come from
As for glitches, dealing with GS.com is such a headache that it's seldom worth the cost of entry.