Apertures in staircase

OS: Win7 Pro
PsychoPy version: 3.1.3
Standard Standalone? : y
What are you trying to achieve?:

What did you try to make it work?:
Dear experts,
I have created an experiment that has a background filled with small gratings with same orientation. The fixation cross appears in the centre of the screen.
As a bottom layer, under the main background, I drew similar background with different orientation.
On both sides of fixation I created two small apertures (circular and triangle) that show the bottom layer background.

The idea is to let participants recognise the two apertures using the different texture (different orientation).

All stimuli are drawn inside a staircase loop.

[…]

for duration in staircase:
   [stuff happening to stimuli]

   aperture1.enabled= True
   stimuli_s1.draw()
   aperture1.enabled= False

   aperture2.enabled= True
   stimuli_s2.draw()
   aperture2.enabled= False
   texture_s.draw()
   fixation.draw()

   win.flip()

[…]

The participant has to press left or right key depending on the position of target (triangle aperture) stimulus.

This is how it looks without staircase:

What specifically went wrong when you tried that?:
I get not specific errors but when I run the script I obtained only the background with fixation. It’s seems that apertures don’t work inside a staircase.

Any suggestion?