Words you knew, yet didn't recognize in print, because of English not being phonetic
This happens most commonly in elementary school, of course.
The one I remembered today was "lemonade." It isn't even very strangely spelled. For some reason I thought the accent was on the second syllable. I thought the <em>e</em> at the end was pronounced, rather than modifying the sound of the <em>a. </em>So, in my mind, I heard "leh-MAHN-a-DEE"--and didn't realize that it was a word I knew well.
Can you think of any examples from your own life?