this has to be a bug...

[Michael ODonnell]

>   $ sudo /sbin/ifconfig eth0:0 del 10.107.33.189
        [...]
>I ask to delete a non-existent interface, and instead, I get
>a totally new one I didn't ask for :)


Though the results aren't what you wanted this might
possibly be a case of RTFM; my man page says,

 "To delete an alias interface use ifconfig eth0:0 down"