If I understand you correctly, yes, that's because Safari literally changes the entire height of the viewport due to the browser chrome becoming visible or hiding. ScrollTrigger does a "soft" refresh in that case, meaning it WAITS until the scrolling stops before it fires its refresh() to re-calculate all the positions, otherwise Safari would suddenly stop the momentum-based scrolling. Either way, you'd have a jump because of the browser resizing everything. That's not a bug in ScrollTrigger. 
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