I was able to reproduce that here and have added it to our list to fix up.
In the meantime, you can use the built-in Monitor Fading feature. On the Settings > Monitor Fading tab, you can set a hotkey on it, set the mode to "Fade all except primary," and then set the opacity to 100%.
Hope that helps!
Just a quick update to let you know that this issue should be all fixed up. We made some changes in the script code itself, so if you re-download it, you should be good to go.
Thanks!