There is a spelling problem when using the all-caps font effect, which I often do with Heading Paragraph Styles.
The font effect capitalizes the word to the eye. But in doing so it prevents auto-correct from capitalizing the word’s first letter, which is normal for the first words of sentences or when the word has been specced in autocorrect. The spell check still sees the underlying lowercase word and flags it as an error.
Here’s an example. I type the word bryan in an all-caps Heading. I see BRYAN, and it is flagged as a spelling error.
If I type bryan anywhere else, it is autocorrected to Bryan, which is in my dictionary and is not flagged as a spelling error.