Actually, its the MythTV_Plugin, living on the dcerouter. I got the clue from this old forum thread http://forum.linuxmce.org/index.php?topic=4496.0
The relevant code can bee seen in the charonmedia trac browser http://svn.charonmedia.org/trac.cgi/browser/trunk/src/MythTV_PlugIn/MythTV_PlugIn.cpp#L976. From what I can make of the wiki documentation about building a 0710 version, that link is not for the correct 0710 source, but I suppose the code is not that different.
Now, when looking at the source, I notice it seems that it is possible to stop the execution of the CMD_Sync_Providers_and_Cards method. Setting the Don't Auto Configure setting for the device (MythTV_Plugin I guess..) would stop the execution before any changes are done. Not sure if this would result in any other problem, as I have not checked the other code in the function. I think it would affect users having tuners in MDs, or probably after changing tuner settings.
I have not yet changed anything in the code, I just tried compiling it. Failing to manage that, it just got put off. But I am very interested in trying again to see if we can get it right :-)