Are you using MAC OS 10.7x (Lion)?
If yes, this issue might be caused due to some third party extensions installed on the system.
Cinch and Flexiglass have particularly been known to have caused this issue. If the issue persists after disabling these extensions, there might be other third party extensions too which are causing this issue.
In order to identify which of the extensions is causing the issue, start by first restarting system without any extensions enabled (to see if the problem is gone) then re-enable each extensions until the offending one has been identified. Some extensions may require being removed; disabling them doesn't stop the bad behaviour. To narrow down the search, start with any extensions that change seeing, hearing, keyboard or mouse/trackpad behavior, or those who require a feature of Universal Access to be enabled.
Once the extension causing this issue is isolated, one can disable it to avoid the issue.