Copy problem in Expyriment

# This script will not show text, but a filled white square where the text
# should be. The problem appears to be that preloaded stimuli cannot be
# copied. The following steps will reliably reproduce the problem across all
# tested configurations.
#
# - Create a fullscreen OpenGL window
# - Preload a stimulus
# - Copy the (same) stimulus

from expyriment import control, stimuli
import time
control.defaults.initialize_delay = 0
control.defaults.open_gl = True
exp = control.initialize()
c = stimuli.Canvas(exp.screen.size)
t = stimuli.TextLine('Some text!')

# Disabling either preload() or copy(), or reversing the order will make the
# script work as expected again.
t.preload()
t2 = t.copy()

t.present()
time.sleep(1)
control.end()