[plt-scheme] finder:get-file question

How do i get the get-file dialog to only show files with a particular
extension?  I've tried this:

(define (foo)
    (parameterize ([finder:default-extension "mcl"]
                   [finder:default-filters '(("MC Level Files" "*.mcl"))])
      (let ((file (finder:get-file #f "Select an MC level file")))
        (printf "~a\n" file))))

But the drop-down listbox next to the filename edit file only shows the
default "Any" (*.*) filter and not the specified filter.  I also tried
specifying a filter regexp (byte-regexp) as the third parameter to get-file,
with no better results.

Thanks much. -- Eric
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