One more Duo apostrophe recognition error:
Duo accepted "The boy's drawing a pink dog" but claimed I "missed a space" in "boy's".
I guess this happens in the reordering word exercise. It seems they simply concatenate each word in answer and join them with a space ([the], [boy], [is] is joint to form [the boy is]; with the same logic, [the] [boy] ['s] becomes [the boy 's])
I guess Duo has already known about this problem but as it isn't stopping correct answers get accepted, they aren't prioritizing fixing it.