We have had an issue raised to us about Migration Tables and GPP that we wanted to take a moment to clarify. What are Migration Tables you might ask?
GPMC provides a mechanism for Importing and Exporting policies. This is especially useful for moving tested GPO's from one forest to another such as from the test network to the production network. Part of the involves whats called a Migration Table. This is essentially a mapping table that allows you to map security principals (users and groups) from one domain to another. It also allows you to map UNC share paths from one domain to another also.
Recently a customer found that the Group Policy Preferences does not work with Migration Tables. This means specifying a Migration Table will have no effect on the security principals from one domain to another with GPP settings and the result is that these will be ignored.
The workaround of this is essentially to manually map them either post-import or to edit the XML exported in the exported policy folder manually or through a script.
Note that this also affects the to be released Advanced Group Policy Management 4.0 solution as it uses the same GPMC APIs and Migration Table functionality that GPMC itself uses.
We know its not a great outcome and are currently looking at options to address this in future.
Michael Kleef, Program Manager