I was double-matching the bold end.

src/parser/text_element_parser.rs

@@ -57,7 +57,6 @@ fn flat_bold<'s, 'r>(i: &'s str, context: &'r OrgModeContext<'r>) -> Res<&'s str
     let (remaining, captured) = recognize(tuple((
         bold_start,
         many_till(text_element_parser, bold_end),
-        bold_end,
     )))(i)?;
     let ret = TextElement::Bold(Bold { contents: captured });
     Ok((remaining, ret))