ok, there are two ways of looking at this:
1) no visible code uses it, and no other reports of the problem, and since @techee already has the fix there is no rush to commit this and it can be committed when @techee publishes his super-plugin
2) since this function is effectively part of the code of `plugin_set_key_group()` (which is the only user, so the fix cannot affect other code, by inspection), and that is in the API, the bug report should be fixed before anyone else uses it
I incline to the second view, so it nobody objects within a few days will commit it.