The only thing I can reach is that Sauron was as confused as we are.
Well, at least we got some ideas, but from what's given I don't know if anything can be 'proven,' beyond the importance of the bigger picture:
Because of Pippin's timely exit from the Palantir Sauron was left in doubt...who has the Ring? Where is the Ring? What are my enemies planning? Do they know something I don't? What are they planning on doing with the Ring? Or if he believed Pippin had the Ring...what is Saruman planning on doing? This only increases when Aragorn reveals himself in the palantir causing Sauron to act more quickly than he had wanted to...because Sauron's got some doubt, and Gandalf thinks it will take him a while to figure out what they are planning, so Gandalf will use that time to his advantage.
