The new lesson is bugged.
@admins please see above
I had no problems completing this lesson though. 
I just went and tried again and it went through fine 
just a gremlin I guess
WK staff are undoubtedly going to want to know: Are you using any scripts?
If so, post a list of the ones that TamperMonkey says are running during your lessons.
Heh… seems someone else is having problems with that exact vocab:
Edit: Ahh, I see there was an issue that was found and now fixed:
Vanilla WK for me! Glad they got it fixed though