Graph interaction in test_interactions exploration broken

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Login as admin and load the test_interactions exploration
2. Play until graph interaction
3. Entering the correct solution for the state graph interaction returns 
"incorrect" (unless I'm missing something)

What is the expected output? What do you see instead?
The correct answer should be recognised to be correct so that it's possible to 
proceed to the next state

Please use labels and text to provide additional information.

Original issue reported on code.google.com by mschmittfull@gmail.com on 6 Aug 2015 at 6:27