Trawling the t’internet late last night I turned up this little MSDN nugget which explains the situation, see paragraph 5 in the Deployment section of the full article.

“Since the configuration data for services on managed classes are stored in the COM+ catalog, certain catalog entries may also be modified administratively after registering an assembly. Some services should not be modified in this manner. For instance, disabling the transaction service in the catalog can cause the code to operate incorrectly. Deployment-specific settings like object construction strings and security roles can be manipulated post registration. XCopy deployment of assemblies containing serviced components may not be sufficient when post registration settings are made. The COM+ application import and export feature helps to distribute the current state of the application. Further information about import and export is provided in the remoting section.

In some cases the catalog is not consulted for configuration data but is extracted purely from the assembly metadata. The cases are for AutoComplete, JIT, Object pooling (although the pool size is extracted from the catalog) and the secure method attribute. More details about this issue are discussed in the sections describing those services.“

The full article can be found at;

Understanding Enterprise Services (COM+) in .NET
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dndotnet/html/entserv.asp