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Using the trackpad on my macbook, when I scroll up (two finger touch/swipe gesture) to the top of the mail list in any folder, about a second or so after it reaches the top, the view scrolls down a few pixels
This occurs regardless of the preview pane position and in my testing occurs on both Chrome and Safari
I'm currently on 13.3 ENT and I'm using El Capitain on my Mac Book Pro
I'll be upgrading to 14.x this week and will update here if the issue is still present.