Gmail's usually flawless system has been throwing spellcheck errors recently:
Notice how in this screenshot, the word is spelled "Photographer" (correct) and the Gmail spellcheck still highlights it in yellow. When I click on it, the top suggestion is EXACTLY the same, spelled "Photographer" still with a capital P and everything.
The gmail forum said to make sure my language hadn't changed. It is (and always has been) set to "English (US)."