If the default key tab exists, it is always used even if a different keytab name is passed in the argument to Ktab.
mission3-41% touch ~/krb5.keytab

mission3-42%
/net/luster/export/scratch/seemam/hopper-new/build/solaris-sparc/bin/ktab
-J-Dsun.security.krb5.debug=true -a rammarti -k FILE:/tmp/keytab
Config name: /etc/krb5/krb5.conf
Password for ###@###.###:test123
>>> KeyTabEntry: key tab entry size is 54
Done!
Service key for rammarti is saved in /home/rammarti/krb5.keytab

mission3-43% rm ~/krb5.keytab
rm: remove /home/rammarti/krb5.keytab (yes/no)? y

mission3-44% !/net
/net/luster/export/scratch/seemam/hopper-new/build/solaris-sparc/bin/ktab
-J-Dsun.security.krb5.debug=true -a rammarti -k FILE:/tmp/keytab
Config name: /etc/krb5/krb5.conf
Password for ###@###.###:test123
>>> KeyTabEntry: key tab entry size is 54
Done!
Service key for rammarti is saved in /tmp/keytab