IF you think you have spotted a bug (or a gremlin!) then let us know here. Try to give as much information as possible so we can track it down. In particular if it is a website issue then say what browser you are using (eg. Chrome on Windows, Safari on iPad etc.) and which version, in case the problem is browser specific.
If you think there is a problem with a challenge then it is better to email us at [email protected] so we can deal with it immediately.