I've been noticing that WordPress likes to nest the "More" tag within other tags instead of putting it between them. So, if you put your cursor at the end of a paragraph, it will put the More tag before the /p tag. If you put it at the beginning of a paragraph, it will put the tag after the p tag. This is bad because if the first word or line of a paragraph is (for example) bold, it will also put it after the B tag, making everything else below it bold because there is no closing /b tag to follow it. If you try to put it before a table, it will actually put it inside the table causing your default posts page to "break" because the browser thinks that everything that follows is inside the table.
I'd like to suggest that this is a bug.