It is one of the worst phenomenon in local organization, that manager usually unable to create a fit between the job description and the job specification, here it comes two scenarios under it when manager made that type of particular mistake and in some cases actually unable to realize that they are making this error and how hard this will effect your organization.These two scenarios are 

Now the first situation is not creating so much trouble as you don't have the required personnels so some how by giving training to the individual and with lesser cost you are able to get your job done. It is not creating a big problem for your organization. 

But in second case which I have realized after experiencing it from a number of organization, I really feel that hiring of an individual with over skilled is creating the liability for your organization. HR manager made this mistake as in current situation where the economy is in recession people are loosing their jobs in such cases they are willing to work for such a post which are below their KSA's (knowledge, skills and abilities) resultantly their motivation level also get decreased as I have already discussed in my previous post (set significant but achievable goals). beside this as job description is not matched with the job specification so people with over skilled keep looking for the other jobs of their caliber in the market and  as they found the job having a great fit they go for quiting the job. In this situation not only the employer has to pay more to the employee for having a number of skills but when they quit the employer also have to bear the turn over cost. So in such a case from the very beginning HR manager must made some rational decision regarding the hiring so that it may able to save a lot of money for the organization.