If "Spell check as you type" is on, typing a space -- or pasting in text that contains spaces -- triggers a wavy red underscore under any misspelled word that's followed by a space. However, if you type a word in the middle of some text (i.e., editing existing text rather than typing some new text) and don't type a space, then navigate away using arrows or home/end or pg up/dn or the mouse, no red underscore is triggered. This is a bug. Also, if you type misspelled word followed by a punctuation mark and no space, this too fails to generate an underscore but should. Strangely, if you paste in such a sequence, an underscore is triggered, as it should be.