For an analogy of the syntactico-semantic difference discussed in Post #4, consider how differently "what he said" is interpreted in the two examples below. A more natural formulation of (a), it should be noted, is "Did he say that he was sad or that he was mad?"
(a) Was what he said that he was sad or that he was mad?
(b) Was what he said surprising or unsurprising?
In (a), the speaker doesn't know what "he" said, but knows that it was either the one thing (that he was sad) or the other (that he was mad). In (b), the speaker may or may not know what "he" said. The question is whether it possessed the quality of being surprising or the quality of being unsurprising.