[2.0.19] Changing quality of Item ghost hovering over some GUI elements does nothing

[joshinils]

change_quality_gui.webm

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In the video, I have opened a decider combinator. I wanted to change the quality of output signal for plates, while hovering over the existing output item slot.
Over the duration of the entire video I am changing quality. I am holding down left alt and using the scroll wheel to scroll up and down, changing quality all the time.
Only on the portions of the GUI (and outside it) which do not contain conditions or output or signals will the quality change.

So I have to specifically not hover the item over the slot where I want to place it so I can change its quality.