Overwriting plugin functions - bug or feature?

Overwriting plugin functions - bug or feature?


My co-worker and I found a bug/feature and wanted to get some feedback
as to the thought behind this "feature".
Situation: On a single page I'm using jQuery via the script tag, then
I add a custom function, and finally I call jQuery again via the
script tag. When I try to run my custom function, it's gone! It seems
that although jQuery will try to use any previously created jQuery
object, jQuery.fn is overwritten every time.
// don't recreate jQuery
var jQuery = window.jQuery = window.$ = function( selector, context )
{ ...
...
// but always overwrite the functions?
jQuery.fn = jQuery.prototype = {...
...
Is there a reason that jQuery.fn is being overwritten?
Thanks,
Adam