I have no real expertise on how to deal with this issue in a gifted child. But Giftodd's post reminded me of a ex-boyfriend of mine who was a linguist. I would ask him to proof read an essay for me and when he had finished tearing through and fixing spelling and grammar I would ask "What did you think?". He would look at me, confused, and reply "Huh?". ME: "What did you think of the essay?" He: "Oh, I didn't READ it. I just fixed it. If you want me to read it you need to tell me first."
For him consuming content and processing the words & grammar were two totally separate interactions with a text. And words and grammar were WAY faster. He was no slouch at actually consuming the content either but the speed at which he "Fixed" was scary. And obviously he was interacting with the text in some sort of meaningful way in order to be able to make all the sentences grammatically perfect, modify paragraph structure, etc. And yet he would have literally zero recall of the content afterward unless he started with the intention of "Reading" it.
Same boyfriend was adamant that good spellers have a "visual check", which I have been meaning to go talk about in a different thread.
And I certainly know that I find myself randomly having NO recollection of what I just read to my child.