Just upgraded to Moodle 3.1.5 and am running it with the latest version of the Mahara portfolio plugin 1.2.1-mdl2.7+ (2015021006).
When teacher goes in to grade the assignment, which students have presumably submitted as a page/collection using Mahara, it displays an "invalid response" error on the grading page and a loading wheel that never stops loading. (see screenshot)
I believe this is an error given the new assignment grading tool. Does anyone have a temporary solution around it?