Preview doesn't update when using script - v1.3 beta

i’m using convert to greyscale script (this one: Understanding Colour Value with HSL/HSV - #3 by Olga_Galvanova ). when i use it, the preview window doesn’t update unless i hide and reveal one of the layers (so i can even start drawing on that layer without any change). it doesn’t matter if i use shortcut or call the script from menu.

edit: if i select a brush and wiggle over the layer created by script without drawing on it, i can reveal it bit by bit as well.