A bug reported about 40 days ago has finally been fixed by Google. The bug was specific to the AdWords API not returning search volume data for certain months. The report was in the Google AdWords API Form and said:

Several users of the API were left stranded for all that time. One said, “My company also relies on this data. I hope this is taken as high priority.” Google did continually come in to tell people they were aware of the issue and engineers are trying to fix it.

The fix came August 2nd, Eric from the Google AdWords API team wrote:

Forum discussion at Google AdWords API Form.