I was working on a different issue through Bugzilla (where when I tried to apply an item to a homework problem, if I changed sets the corresponding list of problem numbers did not update) and Geoff Goehle suggested I try pulling the renamefix branch from his git:
git remote add goehle http://github.com/goehle/webwork2
git pull goehle renamefix
I did this and it seems to have resolved both issues.
WeBWorK Main Forum
errors with Achievement Items
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