However, the good news is that  it seems Google as finally taken note of this matter, a Google spokesperson has confirmed that this was happening due to a bug in the AdWords Keyword Tool.

Here is what a Google representative told Search Engine Land after they asked for confirmation of the issue:

Were aware of a potential issue that is affecting the keyword tool in AdWords, and are working hard to fix it.

Although a list of exact keywords affected was not available it was found that a random selection of keywords were reporting zero for volume including long tail, middle tail, short tail and head keywords were affected at both global and local volumes. A number of popular terms like ipod, dogs and wine, were among the list of affected keywords. Here is a screen shot of the some of the impacted keywords as they appeared in the AdWords keyword tool report.

Some users tried testing to see if this problem was region specific but it seems to be a global problem rather than being confined to any particular continent or country.

Google havent provided a date/time on when they expect this bug to be fixed, but as soon as we know anything more, we will be sure to update this post.