if root's umask os 066, then rpm -Uvh 2.0.5a-1.i386.rpm leads to no group, other read permission on /etc/services, /etc/inetd.conf. In the first case, this breaks (at least) Powell's LPRng, and one supposes will cause trouble in general. See the 'mv' lines in the postuninstall script. In the second case, no trouble identified but it seems unusual.
fixed in samba-2.0.5a-2, which will be in next Raw Hide release.
Unfortunately, since the problem is in the %postun of the *previous* version, you might still have to chmod them back later.
*** Bug 4257 has been marked as a duplicate of this bug. *** I installed the upgrade rpm and it changed permissions on /etc/services from rw-r-r to rw--. As a result, outgoing telnet and ftp broke. I've done this on 2 separate RH6.0 machines, and on the second I observed that the samba rpm actually did cause the problem (before and after comparison)