[Therion] Combining caves using different co-ordinate systems

I have been converting a project from an old datum to a more recent one following the issuing of new maps using the newer datum. So all my entrance GPS coordinates changed. I updated the cs statements in my survey data files and my KML output is still in the correct place. So all was looking good. Then I discovered that if I include a survey in the old cs with one using the new cs then Therion appears to treat both caves as having the same cs. Whichever cs is used by the first included cave is applied to subsequent caves too. Is there a way to deal with this? Footleg