I have always thought this scene very odd also. Surely Mr. Darcy is more at fault here and what better example of the "cut direct" could we recieve?

As others have said, this is partly AD's manipulation of the story to suit his purpose. This sharp cut makes the proposal all the more surprising.

In the novel, JA clearly gives clues that Darcy is intentionally meeting Lizzy and she misinterprets this, as she misinterprets nearly everything he does. Poor Lizzy, always trying to take Mr. Darcy's measure. She is so pride-full of her discernment of personalities and misses the boat completely on Darcy and Wickham.