Sadly the transparent sprite didn't work so I guess it must be a stacked mouse tracking issue, and I found a huge bug in the new Contrast theme: it's missing the "load"/"save" buttons in the dialogue boxes! ๐
UPDATE: I came up with a workaround for the mouse tracking: I made an intermediary, always on simple layer that sits between the two motions (Subtle -> Intermediary -> Exaggerated) and now things work as expected. So it's definitely a problem with consecutive mouse tracking inheriting.
I hope this helps.