i think that previous versions did this as well, but for sure the newest ypserv in 5.3 replaces /var/yp/Makefile with a new copy. needless to say if you've made any changes to that file, you will not be happy. we had a couple hours of phone calls after passwords stopped working. the original file is save as Makefile.rpmsave, so recovery of the file is straightforward. the issue has been flagged upstream and it sounds like it should be fixed before any new updates to ypserv are made. /etc/ypserv.conf is another file that can get overwritten.