I've seen this behavior as well and will escape the closing quote. So your example becomes:
"constraint on objects of type `XXXX`\"
Adding a space is probably cleaner, but I've done this out of habit.
EDIT: I should add that this behavior is one of those that doesn't show up in the Asciidoctor previewer, only on a file rendered by Asciidoctor itself. Maybe Dan or someone else can chime in on this.