The design of the library redistributables merge modules in the various VC9 editions (RTM, SP1, QFE, etc.) will prevent a minor upgrade from being created for a product that was originally distributed with one version of the compiler (e.g., RTM) while the minor upgrade is distributed with another version (e.g., SP1).
This failure exists because the new merge modules create new Windows Installer components for the library files in the update which causes the previous components for the earlier merge module to be removed from the package. This is a fundamental violation of a minor upgrade. Components cannot be removed.
In the past, the library files were only updated in the merge modules. This allowed the updates to work as expected because the component structure for a given compiler version.
Complicated products can be distributed with VC++ and these products may require minor upgrades. With this change, minor upgrades cannot be distributed with VC++ merge modules.