Memberdata.xml vs memberdata_properties.xml

When I export settings from portal_setup I noticed that two settings for member data are exported

They are identical, so what is the difference between memberdata.xml and member data_properties.xml ?

Good question, though they both seem to use the same registry key which leads me to believe either one of these files is simply an old style (or deprecated) method. Similar to the jsregistry.xml and cssregistry.xml.

If this is wrong, then my next best guess would be something indexing related, but I'd need to check further.