Unexpected output of "df -k" command

Hi,
I am running a command "df -k" to check the HDD utilization i am getting some garbage values in output of the command.
Output coming

Filesystem              kbytes         used           avail       capacity                       Mounted on
/dev/dsk/c1t0d0s7    113197651 9223372036900655265       0 8230327472619% /mmf

while expected output is

Filesystem kbytes        used      avail        capacity          Mounted on 
/dev/dsk/c1t0d0s7        113197651 22359874      89705801      20%        /mmf

unable to understand the reason for that, i rebooted the server and then all was well.
Just want to know that why this happened?

Thanks in advance