The /etc/rc.d/init.d/network script looks (egrep's) for ONBOOT=no with or without double quotes, but if you have used *single* quotes, this script does start ifup for that interface. From a user point of view, it then looks like the interface is started (which isn't the case because the ifup script honours the ONBOOT='no' correctly, of course).
This should work as of 6.84-1 or later.