Apple has released iTunes 11.0.5 for download for Mac and Windows users, to address an issue with iTunes in the Cloud some users are experiencing:

This update corrects an issue with iTunes in the Cloud, where some purchases may download or play unexpected items.

The files sizes for individual downloads is as follows: OS X (187.46 MB ) Windows (84.99 MB) Windows64 (86.68 MB). You can find the latest update by going to the Mac App Store and navigating to the Updates tab.