After installing an update from August, specifically KB2918614, you may have found that repairing an already installed application resulted in a UAC prompt. It can be annoying and something you didn’t quite expect, but not truly detrimental to the operation of the application or computer.
Microsoft has been aware of the problem and chose this month's Patch Tuesday to release a fix for the minor issue. The Hotfix, available in KB3008627, is provided for Windows 7, Windows 8, Windows 8.1, Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, and Windows Server 2012 R2.
Users of Windows 8.1 RT or Windows RT can only obtain the Hotfix through Windows Update.
Microsoft describes the cause of the problem like this:
This issue occurs because already installed applications do not have their hash cache created after update 2918614 is installed. When a repair is triggered for these applications, Microsoft Installer (MSI) cannot validate the installation files. Therefore, MSI needs consent from the user to finish the repair.