I think this is substantially a duplicate of bug 1710246. (The title of that one says "when you repeat in the same direction", but the behaviour is the same as "from a static position", i.e. cases where the velocity samples used to determine the starting velocity of the snap-back animation come from when the page is overscrolled rather than when the page is scrolling normally.)
Bug 1713859 Comment 4 Edit History
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I think this is substantially a duplicate of bug 1710246. (The title of that one says "when you repeat in the same direction", but the behaviour is the same as "from a static position", i.e. cases where the position samples used to determine the starting velocity of the snap-back animation come from when the page is overscrolled rather than when the page is scrolling normally.)