Post Editor: Wrap In Box + Horizontal Line Bug

(Sorry for the extra bug reports re: wrap-in box, I suddenly discovered a bunch of new ones!)

There appears to be an issue when using the horizontal line in a wrap-in box. You can see some of the weirdness in the video below, but there’s one major issue I should specifically mention.

If you try to add a horizontal line at the very bottom of a wrap-in box, the post editor will display a new box title section underneath it. You cannot change it to standard text, and hitting the return key does nothing. Hitting backspace will remove the entire wrap-in box, and will continue to delete its orphaned elements upon multiple presses.

Also minor side issue shown from 1:03 in the video; adding a horizontal line within the content area displays a line but makes it highlighted, and typing any text will delete the line.