Google Analytics Filters Shared by Reference

i.e.:
$ga_filter1_on_siteA = 'foo';
$ga_filter1_on_siteB = $ga_filter_on_siteA;
$ga_filter1_on_siteB = 'bar';
print $ga_filter_on_siteA;  // => "bar";

 

WTF.  These filters are copied/shared by reference?  Apparently.