I redirect you post from Windowblinds to Curtains.
Can you post what you see on your Windows using that taskbar buttons. That might help us see what is your issue. It might be just the painting margins setting issues. BTW, the taskbar buttons use 6 image states. I saw you're using 5.
Here is my Simplic Mod Curtains taskbar button for reference.

Thank you,
Basj,
Stardock Community Assistant