You need to tell us what technology you are talking about. The name of the function you're calling is the same as a function in CGI.pm, so I'd guess that you're using CGI.pm to create HTML - but that's not obvious. There could be any number of other technologies that have a similarly named function to create similar widgets.

But assuming that you are talking about CGI.pm and HTML, you need to look at the HTML that's generated. It sounds to me as tho' the width of a list with no items should still be controlled by the width attribute - but that decision will be made by the browser. Are you still generating a valid width attribute when the list is empty?