Yes, sorry about that. CodeRunner 3.7.5 added some extra GraphUI functionality to allow you to provide an answer-preload graph with specified aspects locked, for example to prevent the student from changing edges or edge labels or nodes etc. The bug was a consequence of that - self-loop edges became locked.
You're the first person outside our University ever to ask me about the GraphUI, so I thought the bug would have very little impact. I held back on updating the Moodle repository until I had a more worthwhile set of updates but that doesn't seem to have happened yet - my apologies.