Thanks for the replies and offers of help. It's been a busy day and I haven't had much time to dig into it deeper, but I've just found that it was only happening on a few files which also were behaving the same way in 12, I just happened to open a number of them at first.......which is like getting "heads" 26 times in a row, then tails. So I guess it's a false alarm, however, I've discovered a new issue:
All vectors which had colors from the Roland color palette applied in 12 have been turned to black when opened in X5. Has that been heard of by anyone else?