Performance issues?

When writing my first Racket GUI program, I've noticed that scrolling is really slow, at least when there are many controls in a panel. For example:

#lang racket

(require racket/gui)

(define frame (new frame% [label "Example"]))

(define panel (new horizontal-panel%
                   [parent frame]
                   [style '(auto-hscroll)]))

(define sliders (for/list ([i (in-range 100)])
                  (new slider%
                       [label ""]
                       [min-value 0]
                       [max-value 100]
                       [parent panel]
                       [style '(vertical)])))

(send frame show #t)

Scrolling this window is very sluggish, taking between 1 and several seconds per frame. (This is on a recent AMD CPU, running Debian stable, and X11.)

My understanding is that racket/gui uses GTK3, so to see if this might be an issue with GTK3, I wrote a similar program in Python:

import gi

gi.require_version("Gtk", "3.0")
from gi.repository import Gtk

win = Gtk.Window()

scrolled = Gtk.ScrolledWindow()
scrolled.set_policy(Gtk.PolicyType.AUTOMATIC, Gtk.PolicyType.NEVER)

box = Gtk.Box(spacing=6)

for _ in range(100):
    slider = Gtk.Scale()
    slider.set_orientation(Gtk.Orientation.VERTICAL)
    slider.set_range(0, 100)
    box.add(slider)

win.add(scrolled)
scrolled.add(box)

win.connect("destroy", Gtk.main_quit)
win.show_all()
Gtk.main()

Scrolling this window is perfectly smooth, and it never has trouble keeping up with my mouse cursor at all -- even with 1000 controls.

(This isn't a language-X-versus-language-Y comparison. I'm simply demonstrating that GTK is capable of good performance with this many controls in a window.)

Moving the sliders is also an issue. With the PyGTK version, it's perfectly smooth, and with the racket/gui version, it's not as bad as scrolling but still noticably jerky.

Is there something I'm missing? Racket performance is fine (at least as good as Python, it seems), and GTK performance is fine, but racket/gui is a couple orders of magnitude slower than it seems like it ought to be.

No source file or test is named. Reproduce the Racket GUI example with many controls on Debian/X11, then compare scrolling and slider responsiveness with the supplied PyGTK example; done would require identifying the racket/gui bottleneck and establishing an agreed performance improvement.