I think that @remove_dates should be initialised as my @remove_dates = split /\0/,$query->param{remove}; since CGI.pm returns a single string, not an array.

I don't think that's actually what happens. If you pass a multivalued paramater, (such as a checkbox_group), CGI.pm will return an array.
From perldoc CGI.pm:

 FETCHING THE VALUE OR VALUES OF A SINGLE NAMED PARAMETER:

          @values = $query->param('foo');

                    -or-

          $value = $query->param('foo');

      Pass the param() method a single argument to fetch the value of 
+the
      named parameter. If the parameter is multivalued (e.g. from mult
+iple
      selections in a scrolling list), you can ask to receive an array
+.
      Otherwise the method will return a single value.
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Regards,
davis
Is this going out live?
No, Homer, very few cartoons are broadcast live - it's a terrible strain on the animator's wrist