Aw man, the way MS Word leaves bold/italic markers lying around [the subject of that comic] and greedily applies formatting to stuff you purposefully didn't select, drives me bonkers ... mind you I caught LibreOffice emulating this behaviour the other day (after an update), I hope it can be retamed ...

RIP WordPerfect 'reveal codes'.

Unfortunately, I lost the recipe (18 years is a long time), but I vaguely recall that the first line had markup that got canceled out, and that trying to delete the newline somehow deleted the end tag for that markup instead of the newline. It also happens when pressing delete at the end of the first line.

Show all styles, then select all instances of style where it's bold and/or italic.